Zwitterionic polymer oil-displacing agent with salt response tackifying effect as well as preparation method and application of zwitterionic polymer oil-displacing agent

Abstract

The invention relates to the technical field of oilfield chemistry, and discloses a zwitterionic polymer oil-displacing agent with a salt response tackifying effect as well as a preparation method and an application of the zwitterionic polymer oil-displacing agent. The preparation method of the zwitterionic polymer oil displacement agent with the salt response tackifying effect comprises the following steps: (1) adjusting the pH value of a mixed solution of acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, acryloyloxyethyl trimethyl ammonium chloride and water to 6-8; (2) in an inert atmosphere, carrying out polymerization reaction on the mixed solution in the presence of an initiator; and (3) drying the reaction product obtained in the step (2), and then crushing and grinding. The zwitterionic polymer oil-displacing agent with the salt response tackifying effect, which is prepared by the method disclosed by the invention, can be used for obviously improving the oil-water mobility ratio and improving the sweep efficiency of a displacing fluid and the recovery rate of crude oil in an oil reservoir.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemistry, and in particular to a zwitterionic polymer oil displacement agent with salt-responsive viscosity-increasing effect, a preparation method and an application thereof. Background Art

[0002] Due to the heterogeneity of some reservoirs and the difference in oil-water viscosity, the water injection front becomes irregular. Therefore, the efficiency of conventional water flooding technology decreases, the difficulty of mining gradually increases, and the oil production decreases year by year. Primary and secondary oil recovery methods can no longer meet the growing demand for crude oil. Some oil fields still have great mining potential after water flooding. Polymer flooding is an important method to improve reservoir recovery in tertiary oil recovery. Polymers can be retained in the pores of the reservoir by adsorption and bridging, reducing the effective permeability of water, thereby reducing the water-oil mobility ratio of the reservoir, increasing the sweep coefficient, and improving the reservoir recovery. However, the diffuse double layer of conventional polymers is compressed under high salinity, the negative charge of the polymer molecular chain segments is greatly reduced, the hydrodynamic size of the molecular chain aggregates is reduced, and the thickening ability of water is greatly reduced. At present, the main methods to improve the salt tolerance of polymers are to introduce sulfonic acid groups or rigid side chains, etc. Although the salt tolerance of polymers is effectively improved, there is still a polyelectrolyte effect, which will still be affected in high-salt environments.

[0003] Zwitterionic polymers are mainly divided into two categories. The first category is a polymer monomer with both cationic groups and anionic groups. The second category is a block polymer with the same number of anionic and cationic groups on the molecular chain. There are four main cationic groups that make up zwitterionic polymers: quaternary ammonium salt cations, quaternary phosphonium salt cations, pyridinium ions, and imidazolium ions. There are three main anionic groups: sulfonate anions, carboxylate anions, and phosphate anions. Different cationic groups and anionic groups can construct different zwitterionic polymers. Among them, the combination of quaternary ammonium salt cations and three anions can obtain three types of zwitterionic polymers: sulfonate betaine (SB), carboxylate betaine (CB), and phosphorylcholine (PC). The Zeta potential of both types of zwitterionic polymers is electrically neutral. Compared with other electrically neutral polymers, zwitterionic polymers not only bind to water molecules through hydrogen bonds, but also the electrostatic interaction of the polymer molecular chain enables them to firmly associate with water molecules. In addition, unlike the polyelectrolyte effect exhibited by conventional polymers, zwitterionic polymers exhibit anti-polyelectrolyte effect. The Chinese invention patent with application number 201710947567.3 discloses a salt-responsive modified polyacrylamide oil-displacing agent and a preparation method thereof. The monomers used are acrylamide, sodium acrylate, acrylic acid polyether polyol and acrylic acid polyethylene oxide propylene oxide sodium ethylene sulfate, wherein the acrylamide monomer accounts for 40-90% of the total monomer amount. By changing the salt ion concentration, the ability to interact with crude oil can be changed, so that oil and water can be separated quickly, achieving the effect of rapid demulsification.

[0004] In view of the high-temperature and high-salt oil reservoir environment, current research usually introduces hydrophobic long chains, sulfonic acid groups or cyclic rigid side groups into the polymer molecular chain to improve the polymer's temperature and salt resistance. However, there are still unfavorable factors such as accelerated polymer degradation, decreased polymer toughness, significantly reduced viscosity and high initial viscosity of high molecular weight polymers in high-temperature and high-salt environments. Therefore, it cannot meet the development needs of high-temperature and high-salt oil reservoirs. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem that conventional polymers in the prior art have poor salt resistance due to the polyelectrolyte effect and thus cannot meet the development needs of high-salinity oil reservoirs, and to provide a zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect, a preparation method and an application. The zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect prepared according to the method described in the present invention can significantly improve the oil-water mobility ratio, improve the sweep efficiency of the displacement fluid and the crude oil recovery rate of the oil reservoir.

[0006] In order to achieve the above object, the present invention provides a method for preparing a zwitterionic polymer oil displacement agent having a salt-responsive viscosity-increasing effect, the method comprising the following steps:

[0007] (1) adjusting the pH value of a mixed solution of acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, acryloyloxyethyltrimethylammonium chloride and water to 6-8;

[0008] (2) subjecting the mixed solution to a polymerization reaction in the presence of an initiator under an inert atmosphere;

[0009] (3) drying the reaction product obtained in step (2), and then crushing and grinding it.

[0010] Preferably, in step (1), the mass ratio of the acrylamide, the acrylic acid, the 2-acrylamide-2-methylpropanesulfonic acid and the acryloyloxyethyltrimethylammonium chloride is 1:(0.1-0.3):(3-10):(3-10).

[0011] Preferably, in step (1), the pH value of the mixed solution is adjusted to 6-8 by adding NaOH solution and / or HCl solution.

[0012] Preferably, the concentration of the NaOH solution is 8-12 wt %.

[0013] Preferably, the concentration of the HCl solution is 8-12 wt %.

[0014] Preferably, in steps (1) and (2), the mass ratio of the initiator to the acrylamide is 0.01-0.2:1.

[0015] Preferably, the initiator is ammonium persulfate and / or sodium bisulfite.

[0016] Preferably, in step (2), the polymerization reaction conditions include: temperature of 40-60° C. and time of 7-12 h.

[0017] Preferably, in step (3), the drying conditions include: temperature of 50-80° C. and time of 8-24 h.

[0018] The second aspect of the present invention provides a zwitterionic polymer oil displacement agent having a salt-responsive viscosity-increasing effect prepared by the method described above.

[0019] The third aspect of the present invention provides the use of the zwitterionic polymer oil displacement agent with salt-responsive viscosity increasing effect as described above in the process of recovering crude oil.

[0020] According to the preparation method of the zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect of the present invention, acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and acryloyloxyethyltrimethylammonium chloride are copolymerized by free radical polymerization through redox initiation. The prepared zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect can significantly improve the oil-water mobility ratio, improve the displacement fluid sweep efficiency and the crude oil recovery rate of the oil reservoir. Specifically, the zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect prepared by the method of the present invention can increase the crude oil recovery rate by 56.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of the chemical reaction process for preparing a zwitterionic polymer oil displacement agent having a salt-responsive viscosity-increasing effect according to the present invention;

[0022] Figure 2 This is an infrared spectrum of the zwitterionic polymer oil displacement agent with salt-responsive viscosity-increasing effect prepared in Example 1;

[0023] Figure 3 The microscopic morphology characteristics of the zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect prepared in Example 1 in aqueous solution, wherein (a) is a microscopic morphology characteristics of the zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect prepared in Example 1 in deionized water, and (b) is a microscopic morphology characteristics of the zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect prepared in Example 1 in deionized water with a salinity of 20×10 4 mg / L simulated formation water, (c) is the zwitterionic polymer oil displacement agent with salt-responsive viscosity enhancement prepared in Example 1 at a salinity of 25×10 4 mg / L microscopic morphological characteristics in simulated formation water;

[0024] Figure 4 The rheological properties of the zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect prepared in Example 1 are shown in Figure 1, wherein (a) is the rheological properties of the zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect prepared in Example 1 in the presence of Na with different concentration gradients. + The rheological properties of the solution (b) are the zwitterionic polymer oil displacement agent with salt-responsive viscosity enhancement prepared in Example 1 in the presence of Ca2+ at different concentration gradients. 2+ The rheological properties of the solution, (c) is the zwitterionic polymer oil displacement agent with salt-responsive viscosity enhancement prepared in Example 1 in the presence of different concentration gradients of Mg 2+ Rheological properties of the solution;

[0025] Figure 5 1 is a plugging performance diagram of the zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect prepared in Example 1, (a) is a pressure characteristic curve diagram of polyacrylamide and the zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect prepared in Example 1, and (b) is a crude oil recovery curve diagram of polyacrylamide and the zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect prepared in Example 1. DETAILED DESCRIPTION

[0026] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0027] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0028] The method for preparing the zwitterionic polymer oil displacement agent with salt-responsive viscosity-increasing effect of the present invention comprises the following steps:

[0029] (1) adjusting the pH value of a mixed solution of acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, acryloyloxyethyltrimethylammonium chloride and water to 6-8;

[0030] (2) subjecting the mixed solution to a polymerization reaction in the presence of an initiator under an inert atmosphere;

[0031] (3) drying the reaction product obtained in step (2), and then crushing and grinding it.

[0032] In step (1), the mass ratio of the acrylamide, the acrylic acid, the 2-acrylamide-2-methylpropanesulfonic acid and the acryloyloxyethyltrimethylammonium chloride can be 1: (0.1-0.3): (3-10): (3-10). In a preferred case, the mass ratio of the acrylamide, the acrylic acid, the 2-acrylamide-2-methylpropanesulfonic acid and the acryloyloxyethyltrimethylammonium chloride is 1: (0.15-0.25): (2-8): (2-8).

[0033] In step (1), the pH value of the mixed solution can be adjusted to 6-8 by adding NaOH solution and / or HCl solution. In a preferred case, the pH value of the mixed solution can be adjusted to 6.5-7.5 by adding NaOH solution and / or HCl solution. Further preferably, the concentrations of the NaOH solution and the HCl solution are 8-12% by weight, preferably 9-11% by weight, respectively.

[0034] In steps (1) and (2), the mass ratio of the initiator to the acrylamide may be 0.01-0.2:1, preferably 0.05-0.15:1, and more preferably 0.1-0.13:1.

[0035] In the method of the present invention, the initiator may be ammonium persulfate and / or sodium bisulfite. In the most preferred embodiment, the initiator is a mixture of ammonium persulfate and sodium bisulfite, and specifically, in the mixture of ammonium persulfate and sodium bisulfite, the mass ratio of the ammonium persulfate to the sodium bisulfite is 1:0.5-1.5.

[0036] In step (2), the polymerization reaction conditions may include: a temperature of 40-60° C. and a time of 7-12 hours. In a preferred case, the polymerization reaction conditions include: a temperature of 45-55° C. and a time of 8-10 hours. The polymerization reaction may be carried out in various conventional reaction devices.

[0037] In the method of the present invention, the inert atmosphere can be provided by nitrogen and / or an inert gas. In a more preferred embodiment, the inert atmosphere is provided by nitrogen.

[0038] In step (2), the specific operation process of the polymerization reaction may include: adding the mixed solution to a reaction device, introducing nitrogen for 1-2 hours to remove the air in the reaction device, adding an initiator and heating to a target temperature for reaction.

[0039] In step (3), the drying conditions may include: a temperature of 50-80°C and a time of 8-24 hours. In a preferred case, the drying conditions include: a temperature of 55-70°C and a time of 10-15 hours. The drying process may be carried out in a vacuum oven.

[0040] In step (3), the crushing and grinding process can be carried out in a crusher at a rotation speed of 5400-1000 r / min.

[0041] In step (3), the treatment process of the reaction product may further include: washing the reaction product, then cutting it into pieces, and then drying and crushing and grinding it. The reagent used for the washing may be at least one of ethanol, isopropanol and n-butanol. In the most preferred embodiment, the reagent used for the washing is ethanol. The washing process may be one or more times, preferably multiple times, and most preferably three times.

[0042] like Figure 1 As shown, the zwitterionic polymer oil displacement agent with salt-responsive viscosity-increasing effect prepared by the method described in the present invention is generated by polymerization reaction of the acrylamide, the acrylic acid, the 2-acrylamide-2-methylpropane sulfonic acid and the acryloyloxyethyl trimethyl ammonium chloride, wherein the acrylamide is the main chain of the molecular chain, and the 2-acrylamide-2-methylpropane sulfonic acid and the acryloyloxyethyl trimethyl ammonium chloride are functional side chains. The sulfonic acid group in the 2-acrylamide-2-methylpropane sulfonic acid and the sulfonic acid group and quaternary ammonium salt contained in the acryloyloxyethyl trimethyl ammonium chloride have strong hydrophilicity, which can improve the swelling ability in a high-salt environment while forming a thicker hydration layer, prevent ion-induced precipitation or degradation, and have strong stability in a high-salt environment. The acrylic acid has a strong molecular polarity, which can improve the rigidity and toughness of the polymer molecular chain. In a high-salt environment, the -SO 3 - With -N + The electrostatic attraction is weakened, which can stretch the polymer molecular chains, enhance the association between the molecular chains, increase the size of the molecular chain aggregates, and increase the spatial structure strength and density.

[0043] The present invention also provides a zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect prepared by the above method. The zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect has good salt response and strong tolerance to calcium and magnesium ions, and can significantly improve the oil-water mobility ratio, improve the sweep efficiency of the displacement fluid and the recovery rate of crude oil in the oil reservoir.

[0044] The present invention also provides the use of the above-mentioned zwitterionic polymer oil displacement agent with salt-responsive viscosity-increasing effect in the oil recovery process. In the actual application process, the zwitterionic polymer oil displacement agent with salt-responsive viscosity-increasing effect can increase the recovery rate by 56.8%.

[0045] The following examples further illustrate the zwitterionic polymer oil displacement agent with salt-responsive viscosity enhancement, preparation method and application of the present invention. The examples are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0046] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0047] Example 1

[0048] (1) 2.6 g of acrylamide, 0.4 g of acrylic acid, 14 g of 2-acrylamide-2-methylpropanesulfonic acid and 13 g of acryloyloxyethyltrimethylammonium chloride were added to deionized water and mixed evenly. A 10 wt % NaOH solution was continuously added dropwise. The pH value of the mixed solution was tested with a pH meter and the pH value of the mixed solution was adjusted to 7.2.

[0049] (2) The mixed solution after adjusting the pH value in step (1) was transferred to a three-necked flask, nitrogen was introduced for 1 hour to remove the air, and then 0.13 g of ammonium persulfate and 0.13 g of sodium bisulfite were added, and the mixture was heated to 45° C. and reacted for 10 hours.

[0050] (3) The reaction product of step (2) was washed three times with anhydrous ethanol, then shredded into granules, placed in a vacuum drying oven and dried at 60° C. for 12 h, and then pulverized and ground in a pulverizer to obtain the zwitterionic polymer oil-displacing agent A1 with salt-responsive viscosity-increasing effect of the present invention. Figure 2 The infrared spectrum of zwitterionic polymer oil-displacing agent A1 with salt-responsive viscosity-increasing effect is shown. Figure 3 (a) shows the microscopic morphology characteristics of zwitterionic polymer oil-displacing agent A1 with salt-responsive viscosity-increasing effect in deionized water; Figure 3 (b) shows the salt-responsive viscosity-enhancing effect of zwitterionic polymer flooding agent A1 at a salinity of 20×10 4 mg / L microscopic morphological characteristics in simulated formation water; Figure 3 (c) shows that the zwitterionic polymer flooding agent A1 with salt-responsive viscosity enhancement has a salinity of 25×10 4 Microscopic morphological characteristics of the simulated formation water at 100 mg / L.

[0051] Example 2

[0052] (1) 2.3 g of acrylamide, 0.5 g of acrylic acid, 16 g of 2-acrylamide-2-methylpropanesulfonic acid and 10 g of acryloyloxyethyltrimethylammonium chloride were added to deionized water and mixed evenly. A 9 wt % NaOH solution was continuously added dropwise. The pH value of the mixed solution was tested with a pH meter and the pH value of the mixed solution was adjusted to 7.0.

[0053] (2) The mixed solution after adjusting the pH value in step (1) was transferred to a three-necked flask, nitrogen was introduced for 1 hour to remove the air, and then 0.1 g of ammonium persulfate and 0.15 g of sodium bisulfite were added, and the mixture was heated to 50° C. and reacted for 12 hours.

[0054] (3) The reaction product of step (2) is washed three times with anhydrous ethanol, then chopped into granules, placed in a vacuum drying oven and dried at 65° C. for 15 h, and then crushed and ground in a pulverizer to obtain the zwitterionic polymer oil-displacing agent A2 with salt-responsive viscosity-increasing effect of the present invention.

[0055] Example 3

[0056] (1) 2.8 g of acrylamide, 0.5 g of acrylic acid, 12 g of 2-acrylamide-2-methylpropanesulfonic acid and 14 g of acryloyloxyethyltrimethylammonium chloride were added to deionized water and mixed evenly. A NaOH solution with a concentration of 11 wt % was continuously added dropwise. The pH value of the mixed solution was tested with a pH meter and the pH value of the mixed solution was adjusted to 6.9.

[0057] (2) The mixed solution after adjusting the pH value in step (1) was transferred to a three-necked flask, nitrogen was introduced for 1 hour to remove the air, and then 0.12 g of ammonium persulfate and 0.15 g of sodium bisulfite were added, and the mixture was heated to 55° C. and reacted for 7 hours.

[0058] (3) The reaction product of step (2) is washed three times with anhydrous ethanol, then chopped into granules, placed in a vacuum drying oven and dried at 70° C. for 15 h, and then pulverized and ground in a pulverizer to obtain the zwitterionic polymer oil-displacing agent A3 with salt-responsive viscosity-increasing effect of the present invention.

[0059] Example 4

[0060] A zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect was prepared according to the method of Example 1, except that in step (1), the pH value of the mixed solution was adjusted to 6.5, thereby obtaining a zwitterionic polymer oil-displacing agent A4 with salt-responsive viscosity-increasing effect of the present invention.

[0061] Example 5

[0062] A zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect was prepared according to the method of Example 1, except that in step (1), the pH value of the mixed solution was adjusted to 7.5, thereby obtaining a zwitterionic polymer oil-displacing agent A5 with salt-responsive viscosity-increasing effect of the present invention.

[0063] Example 6

[0064] A zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect was prepared according to the method of Example 1, except that in step (2), the added amounts of ammonium persulfate and sodium bisulfite were adjusted to 0.05 g, respectively, to obtain a zwitterionic polymer oil-displacing agent A6 with salt-responsive viscosity-increasing effect of the present invention.

[0065] Example 7

[0066] A zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect was prepared according to the method of Example 1, except that in step (2), the added amounts of ammonium persulfate and sodium bisulfite were adjusted to 0.25 g, respectively, to obtain a zwitterionic polymer oil-displacing agent A7 with salt-responsive viscosity-increasing effect of the present invention.

[0067] Comparative Example 1

[0068] A zwitterionic polymer oil-displacing agent with salt-responsive viscosity-increasing effect was prepared according to the method of Example 1, except that in step (1), the pH value of the mixed solution was adjusted to 9, thereby obtaining a zwitterionic polymer oil-displacing agent D1 with salt-responsive viscosity-increasing effect.

[0069] Comparative Example 2

[0070] A zwitterionic polymer oil-displacing agent having a salt-responsive viscosity-increasing effect was prepared according to the method of Example 1, except that in step (1), acryloyloxyethyltrimethylammonium chloride was replaced with dimethyldiallylammonium chloride to obtain a zwitterionic polymer oil-displacing agent D2 having a salt-responsive viscosity-increasing effect.

[0071] Comparative Example 3

[0072] A zwitterionic polymer oil-displacing agent having a salt-responsive viscosity-increasing effect was prepared according to the method of Example 1, except that in step (1), acryloyloxyethyltrimethylammonium chloride was replaced with allyltrimethylammonium chloride to obtain a zwitterionic polymer oil-displacing agent D3 having a salt-responsive viscosity-increasing effect.

[0073] Test Case

[0074] The various properties of the zwitterionic polymer oil displacement agents with salt-responsive viscosity-increasing effect prepared in the above examples and comparative examples were tested according to the following methods.

[0075] (1) Viscosity property test: The zwitterionic polymer oil displacement agents with salt-responsive viscosity enhancement of Examples 1-6 and Comparative Examples 1-3 were respectively treated with deionized water and simulated formation water (mineralization degree of 20×10 4 The polymer solutions were prepared with the contents of 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt% and 1 wt% (5000 mg / L, 5000 mg / L for calcium ion and 5000 mg / L for magnesium ion respectively). The viscosity characteristics of the prepared polymer solutions were tested using a Haake Mars 60 (Thermofisher, Germany) rheometer.

[0076] (2) Rheological property test: The zwitterionic polymer flooding agent A1 with salt-responsive viscosity-increasing effect was used with different concentration gradients of Na + , Ca 2+ or Mg 2+ The aqueous solution was prepared into a polymer solution with a concentration of 0.2 wt %, containing Na + The concentrations of the aqueous solutions are 0 mg / L, 5000 mg / L, 10000 mg / L, 30000 mg / L, 50000 mg / L, 100000 mg / L, 150000 mg / L and 200000 mg / L. 2+ or Mg 2+ The concentrations of the aqueous solutions were 0 mg / L, 500 mg / L, 1000 mg / L, 2000 mg / L, 3000 mg / L, 4000 mg / L and 5000 mg / L. The rheological properties of the prepared polymer solutions were tested using a Haake Mars 60 (Thermofisher, Germany) rheometer under the following test conditions: shear rate of 0-100 s -1 , the aging temperature is 130℃ and the aging time is 7d.

[0077] (3) Plugging performance test: By conducting displacement tests on core samples with different polymers, the effects of polyacrylamide (molecular weight 1000W, purchased from Shanghai MacLean Biochemical Co., Ltd.) and zwitterionic polymer flooding agent A1 with salt-responsive viscosity enhancement on improving the recovery of high-permeability sandstone reservoirs under low temperature and high salt conditions were evaluated. The specific test steps were as follows: (1) The core samples were dried at 65°C for 24 hours, and the initial oil saturation was established by vacuum pressurizing saturated crude oil; (2) Water flooding tests were carried out, and the core samples were all treated with a mineralization of 20×10 4mg / L simulated formation water was used for displacement. The injection pressure and oil recovery efficiency were recorded during the test. The test conditions included: tracking confining pressure of 2MPa, back pressure of 0.5MPa, temperature of 130℃, injection rate of 0.5mL / min, and replacement of displacement solution when the injection pressure was stable at each stage; (3) polymer flooding test was carried out, in which core 1 was displaced with polyacrylamide, and core 2 was displaced with zwitterionic polymer oil recovery agent A1 with salt-responsive viscosity enhancement effect. The test conditions included: tracking confining pressure of 2MPa, back pressure of 0.5MPa, temperature of 130℃, and injection rate of 0.5mL / min.

[0078] The viscosity characteristics test results of the zwitterionic polymer oil-displacing agents with salt-responsive viscosity-increasing effect in deionized water of Examples 1-6 and Comparative Examples 1-3 are shown in Table 1. The viscosity characteristics of the zwitterionic polymer oil-displacing agents with salt-responsive viscosity-increasing effect in simulated formation water of Examples 1-6 and Comparative Examples 1-3 are shown in Table 2. Figure 4 As shown, Figure 4 (a) shows the zwitterionic polymer flooding agent A1 with salt-responsive viscosity enhancement in the presence of different concentration gradients of Na + Rheological properties of the solution, Figure 4 (b) shows the salt-responsive viscosifying effect of zwitterionic polymer flooding agent A1 in the presence of different concentration gradients of Ca 2+ Rheological properties of the solution, Figure 4 (c) shows the salt-responsive viscosifying effect of zwitterionic polymer flooding agent A1 in the presence of different concentration gradients of Mg 2+ Rheological properties of the solution. Figure 5 The plugging performance diagram of zwitterionic polymer flooding agent A1 with salt-responsive viscosity enhancement is shown in Figure 2. Figure 5 (a) shows the pressure characteristic curves of the conventional polymer and the zwitterionic polymer oil displacement agent A1 with salt-responsive viscosity enhancement, Figure 5 (b) shows the crude oil recovery curves of polyacrylamide and zwitterionic polymer oil-displacing agent A1 with salt-responsive viscosity-increasing effect.

[0079] Table 1

[0080]

[0081] Table 2

[0082]

[0083] Through Table 1, Table 2, Figure 4 and Figure 5The results show that the zwitterionic polymer oil displacement agent with salt-responsive viscosity-increasing effect prepared according to the method described in the present invention can significantly improve the oil-water mobility ratio, increase the displacement fluid sweep efficiency and the oil recovery rate of the oil reservoir.

[0084] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing a zwitterionic polymer oil displacement agent having a salt-responsive viscosity-increasing effect, characterized in that: The method comprises the following steps: (1) adjusting the pH value of a mixed solution of acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, acryloyloxyethyltrimethylammonium chloride and water to 6-8; (2) subjecting the mixed solution to a polymerization reaction in the presence of an initiator under an inert atmosphere; (3) drying the reaction product obtained in step (2), and then crushing and grinding it.

2. The method according to claim 1, characterized in that In step (1), the mass ratio of the acrylamide, the acrylic acid, the 2-acrylamide-2-methylpropanesulfonic acid and the acryloyloxyethyltrimethylammonium chloride is 1:(0.1-0.3):(3-10):(3-10).

3. The method according to claim 1 or 2, characterized in that: In step (1), the pH value of the mixed solution is adjusted to 6-8 by adding NaOH solution and / or HCl solution.

4. The method according to claim 1 or 3, characterized in that: The concentration of the NaOH solution is 8-12 wt %; and / or The concentration of the HCl solution is 8-12 wt %.

5. The method according to claim 1, characterized in that: In steps (1) and (2), the mass ratio of the initiator to the acrylamide is 0.01-0.2:

1.

6. The method according to claim 1 or 5, characterized in that: The initiator is ammonium persulfate and / or sodium bisulfite.

7. The method according to claim 1, 5 or 6, characterized in that: In step (2), the polymerization reaction conditions include: temperature of 40-60° C. and time of 7-12 h.

8. The method according to claim 1, characterized in that In step (3), the drying conditions include: temperature of 50-80°C and time of 8-24h.

9. A zwitterionic polymer oil displacement agent having salt-responsive viscosity-increasing effect prepared by the method according to any one of claims 1 to 8.

10. Use of the zwitterionic polymer oil displacement agent with salt-responsive viscosity increasing effect as claimed in claim 9 in the process of recovering crude oil.

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