A polyacrylamide for oil displacement, its preparation method and application

Abstract

The present invention belongs to the technical field of tertiary oil recovery, and particularly relates to a polyacrylamide for oil displacement, a preparation method thereof and an application. The preparation method is as follows: The reactor is purged with nitrogen, and laurylamine dipropylenediamine, ethanol and allyl chloride are added in sequence, stirred evenly, and heated for heat preservation reaction; Deionized water, acrylamide, [3-(methacryloylamino)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, undecylenic acid and OP-10 are added and stirred until dissolved; The initiator is added to the high-position dropping tank and dropped into the reaction kettle, and the reaction is continued, the temperature is raised by heating, the heat preservation reaction is carried out, and the temperature is lowered to below 40 °C; The above-mentioned mixed solution is dried and granulated to obtain the polyacrylamide for oil displacement. The polyacrylamide for oil displacement of the present invention has the characteristics of high apparent viscosity, good viscosity reduction effect and shear resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of tertiary oil recovery, and particularly relates to a polyacrylamide for oil displacement, a preparation method thereof and an application thereof. Background Art

[0002] In enhanced oil recovery (EOR) technology, chemical flooding, especially polymer flooding, has become the core means to improve oil recovery due to its low cost and wide applicability. Polyacrylamide (PAM), as the most commonly used oil-displacing polymer, significantly expands the swept volume by increasing the viscosity of the aqueous phase and improving the mobility ratio.

[0003] However, polyacrylamide is prone to hydrolysis in formation water and is also sensitive to some ions in formation water. Therefore, the viscosity of the polymer will quickly decrease. In addition, after the polymer solution undergoes strong shear in the reservoir pores, the polymer molecular chains will deform and break, resulting in a rapid decrease in the viscosity of the polymer solution. The polymer solution will flow along the large pores of the reservoir, reducing the sweep coefficient of the profile control polymer and thus affecting the oil displacement effect. Therefore, polyacrylamide with significant viscosity-increasing effect, good high-temperature and high-salt resistance, shear resistance, good thermal stability, which can effectively increase the viscosity of the displacement fluid, improve the sweep coefficient and increase the swept volume, is the goal pursued by scientific researchers.

[0004] CN104448129B discloses a high-temperature resistant hydrolysis copolymer for oil fields, a preparation method thereof and an application thereof in oil production. By using the high-temperature resistant hydrolysis copolymer, the problem of poor hydrolysis stability of polyacrylamide under high-temperature and high-salinity conditions in the prior art is better solved. It can be used in oil production in oil fields. However, there is no surfactant group in the molecular structure of this invention, and it only has the ordinary polymer oil displacement function, unable to reduce the oil-water interfacial tension and unable to emulsify and reduce viscosity, thus affecting the recovery rate.

[0005] CN103739758A discloses a preparation method of polyacrylamide for oil fields. The steps of the preparation method are as follows: take an acrylamide aqueous solution with a mass concentration of 23-30%, add a cosolvent and stir to mix evenly, add an acid to adjust the pH value to 6-7, cool down to 2-5°C, introduce nitrogen to remove oxygen in the system. When the oxygen content in the system is less than 0.001%, successively add an azo initiator, a complexing agent, a high-efficiency chain transfer agent, a reducing agent, an oxidizing agent. After the system reacts, seal it, keep it warm in a water bath at 80°C for 1-2 h, take out the colloid, crush it, add an inorganic base, hydrolyze it at 70-90°C for 1-2 h, and finally dry and crush the colloid to obtain high-molecular and high-viscosity polyacrylamide for oil fields; the polymerization operation is convenient, the reaction time is short, and the production cycle is shortened; the product has good solubility and filterability, fully meeting the standards of tertiary oil recovery in oil fields. However, the viscosity-increasing effect of this invention in high-salinity reinjection water is not good, affecting its effect. Summary of the Invention

[0006] The present invention provides a polyacrylamide for oil displacement, its preparation method and application in view of the above-mentioned deficiencies of the prior art. The polyacrylamide for oil displacement of the present invention has the characteristics of high apparent viscosity, good viscosity reduction effect and shear resistance.

[0007] In order to achieve the above object, one of the objects of the present invention discloses a polyacrylamide for oil displacement, and the molecular structural formula of the polyacrylamide is as follows:

[0008] ,

[0009] Wherein:

[0010] o = 2000 - 20000;

[0011] m = 20000 - 400000;

[0012] n = 2000 - 80000;

[0013] p = 1000 - 40000.

[0014] In the present invention, preferably, the viscosity-average molecular weight of the polyacrylamide is 35000000 - 50000000.

[0015] Another object of the present invention discloses a preparation method of the above-mentioned polyacrylamide for oil displacement, and the specific steps of the preparation method are as follows:

[0016] (1) Purge the reactor with nitrogen for 6 - 8 min, and successively add laurylamine dipropylenediamine, ethanol, and allyl chloride, stir evenly, heat and keep warm for reaction, and maintain the pH at 7 - 8 with sodium hydroxide solution during the reaction;

[0017] (2) Distill off ethanol under reduced pressure, add deionized water, acrylamide, [3-(methacryloylamino)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, undecylenic acid, and OP-10, stir to dissolve, adjust the pH to 7 - 8 with sodium hydroxide, purge the reactor with nitrogen to displace the air in the reaction kettle, and continuously introduce nitrogen during the subsequent synthesis process;

[0018] (3) Add the initiator to the high-level dropping tank and drop it into the reaction kettle. During the dropping process, the solution automatically heats up, continue the reaction for 1 - 4 h, heat up to 60 - 70 °C, keep warm for reaction for 2 - 8 h, cool down to below 40 °C, and adjust the pH to 7 - 8 with sodium hydroxide;

[0019] (4) Dry and granulate the above-mentioned mixed solution to obtain the polyacrylamide for oil displacement.

[0020] In the present invention, preferably, the molar ratio of allyl chloride, acrylamide, [3-(methacrylamido)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide, undecylenic acid to laurylamine dipropylenediamine is 1.6 - 2.4:10 - 20:1 - 4:0.5 - 2:1.

[0021] In the present invention, preferably, in step (1), the weight ratio of ethanol to laurylamine dipropylenediamine is 10 - 20:1.

[0022] In the present invention, preferably, in step (1), the heating and heat preservation reaction temperature is 60 - 80 °C, and the time is 1 - 4 h.

[0023] In the present invention, preferably, in step (2), the weight ratio of deionized water, OP-10 to laurylamine dipropylenediamine is 20 - 40:0.2 - 0.4:1.

[0024] In the present invention, preferably, in step (3), the initiator is a mixed solution of persulfate and sodium bisulfite, wherein the concentration of persulfate is 10 - 12 wt%, the concentration of sodium bisulfite is 3 - 5 wt%, and the weight ratio of the initiator to laurylamine dipropylenediamine is 1 - 4:1.

[0025] Preferably, the persulfate is one of potassium persulfate, ammonium persulfate, and sodium persulfate.

[0026] The synthesis reaction equation of the polyacrylamide for enhanced oil recovery in the present invention is as follows:

[0027]

[0028]

[0029]

[0030] The third object of the present invention discloses the application of the above polyacrylamide in polymer flooding.

[0031] The polyacrylamide for oil displacement in the present invention is a network polymer with acrylamide as the main body, having a relatively high viscosity, good profile control effect, and containing multiple lipophilic and hydrophilic groups. The lipophilic groups are polyethylene chains and dodecyl groups, among which the dodecyl group is a flexible long-chain lipophilic group that can penetrate deep into the crude oil and combine fully with the crude oil; the hydrophilic groups include carboxyl groups, sulfonic acid groups, and quaternary ammonium salts, which can reduce the oil-water interfacial tension, emulsify the crude oil to reduce its viscosity, transfer the stripped crude oil to the aqueous phase. In particular, undecanoic acid belongs to a flexible long-chain hydrophilic group that can better enter the aqueous phase, so that the emulsified crude oil is produced along with the aqueous phase; the molecule also contains quaternary ammonium salts with bactericidal effects, which can prevent the damage of microorganisms to the polymer during the oil displacement process, especially in low-temperature reservoirs, and assist in improving the crude oil recovery rate.

[0032] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0033] (1) The polyacrylamide for oil displacement in the present invention has a relatively high surface viscosity. At 60 °C, the viscosity at a concentration of 1500 mg / L reaches 120 mPa·s or more;

[0034] (2) The polyacrylamide for high-temperature oil displacement in the present invention has a good high-temperature viscosity reduction effect. At a concentration of 1000 mg / L and 75 °C, the viscosity reduction rate for crude oil with a viscosity of 13200 mPa·s reaches more than 98%;

[0035] (3) The polyacrylamide for oil displacement in the present invention has shear resistance. After 2 hours of shearing, the viscosity retention rate reaches 91% or more. Specific embodiments

[0036] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0037] The following further illustrates the technical solutions of the present invention in combination with specific embodiments:

[0038] Example 1

[0039] (1) Purge the reactor with nitrogen for 6 minutes, sequentially add 0.05 mol of laurylamine dipropylenediamine, 299 g of ethanol, and 0.12 mol of allyl chloride, stir evenly, heat to 60 °C, and keep the reaction for 4 hours. During the reaction, maintain the pH at 7-8 with sodium hydroxide solution;

[0040] (2) Ethanol was removed by vacuum distillation, and 598 g of deionized water, 1 mol of acrylamide, 0.05 mol of [3-(methacrylamido)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide, 0.025 mol of undecenoic acid, and 3 g of OP-10 were added. After stirring to dissolve, the pH was adjusted to 7 - 8 with sodium hydroxide. The reactor was purged with nitrogen to displace the air in the reaction kettle, and nitrogen was continuously introduced throughout the subsequent synthesis process;

[0041] (3) 59.8 g of initiator, which contained 10 wt% of potassium persulfate and 3 wt% of sodium bisulfite, was added to the dropping funnel at a high position and dropped into the reaction kettle. During the dropping process, the solution automatically heated up. The reaction continued for 1 h, then the temperature was raised to 70 °C and kept for 2 h, and then cooled to below 40 °C. The pH was adjusted to 7 - 8 with sodium hydroxide;

[0042] (4) The above-mentioned mixed solution was dried and granulated to obtain polyacrylamide for enhanced oil recovery.

[0043] Example 2

[0044] (1) The reactor was purged with nitrogen for 6 min, and 0.05 mol of laurylamine dipropylenediamine, 149.5 g of ethanol, and 0.08 mol of allyl chloride were added in sequence. After stirring evenly, it was heated to 65 °C and kept for 4 h. During the reaction, the pH was maintained at 7 - 8 with sodium hydroxide solution;

[0045] (2) Ethanol was removed by vacuum distillation, and 544 g of deionized water, 0.9 mol of acrylamide, 0.08 mol of [3-(methacrylamido)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide, 0.035 mol of undecenoic acid, and 3.4 g of OP-10 were added. After stirring to dissolve, the pH was adjusted to 7 - 8 with sodium hydroxide. The reactor was purged with nitrogen to displace the air in the reaction kettle, and nitrogen was continuously introduced throughout the subsequent synthesis process;

[0046] (3) 50.3 g of initiator, which contained 10 wt% of potassium persulfate and 3 wt% of sodium bisulfite, was added to the dropping funnel at a high position and dropped into the reaction kettle. During the dropping process, the solution automatically heated up. The reaction continued for 4 h, then the temperature was raised to 60 °C and kept for 8 h, and then cooled to below 40 °C. The pH was adjusted to 7 - 8 with sodium hydroxide;

[0047] (4) The above-mentioned mixed solution was dried and granulated to obtain polyacrylamide for enhanced oil recovery.

[0048] Example 3

[0049] (1) The reactor was purged with nitrogen for 6 min, and 0.05 mol of laurylamine dipropylenediamine, 243 g of ethanol, and 0.09 mol of allyl chloride were added in sequence. After stirring evenly, it was heated to 70 °C and kept for ɪ h. During the reaction, the pH was maintained at 7 - 8 with sodium hydroxide solution;

[0050] (2) Ethanol was distilled off under reduced pressure, 504 g of deionized water, 0.8 mol of acrylamide, 0.1 mol of [3-(methacrylamido)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide, 0.04 mol of undecylenic acid, and 3.8 g of OP-10 were added, stirred and dissolved, the pH was adjusted to 7 - 8 with sodium hydroxide, the reactor was purged with nitrogen to displace the air in the reaction kettle, and nitrogen was continuously introduced during the subsequent synthesis process;

[0051] (3) 14.95 g of initiator containing 12 wt% of sodium persulfate and 5 wt% of sodium bisulfite was added to the high-level dropping tank and dropped into the reaction kettle. During the dropping process, the solution automatically heated up, and the reaction continued for 2 h. Then it was heated to 65 °C and kept at this temperature for 4 h, and then cooled to below 40 °C, and the pH was adjusted to 7 - 8 with sodium hydroxide;

[0052] (4) The above-mentioned mixed solution was dried and granulated to obtain polyacrylamide for enhanced oil recovery.

[0053] Example 4

[0054] (1) The reactor was purged with nitrogen for 7 min, 0.05 mol of laurylamine dipropylenediamine, 276 g of ethanol, and 0.11 mol of allyl chloride were added in sequence, stirred evenly, heated to 80 °C, and kept at this temperature for 2 h. During the reaction, the pH was maintained at 7 - 8 with sodium hydroxide solution;

[0055] (2) Ethanol was distilled off under reduced pressure, 436 g of deionized water, 0.7 mol of acrylamide, 0.14 mol of [3-(methacrylamido)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide, 0.05 mol of undecylenic acid, and 4 g of OP-10 were added, stirred and dissolved, the pH was adjusted to 7 - 8 with sodium hydroxide, the reactor was purged with nitrogen to displace the air in the reaction kettle, and nitrogen was continuously introduced during the subsequent synthesis process;

[0056] (3) 21.7 g of initiator containing 12 wt% of sodium persulfate and 4 wt% of sodium bisulfite was added to the high-level dropping tank and dropped into the reaction kettle. During the dropping process, the solution automatically heated up, and the reaction continued for 3 h. Then it was heated to 60 °C and kept at this temperature for 8 h, and then cooled to below 40 °C, and the pH was adjusted to 7 - 8 with sodium hydroxide;

[0057] (4) The above-mentioned mixed solution was dried and granulated to obtain polyacrylamide for enhanced oil recovery.

[0058] Example 5

[0059] (1) Purge the reactor with nitrogen for 7 min, then successively add 0.05 mol of laurylamine dipropylenediamine, 204 g of ethanol, and 0.095 mol of allyl chloride. Stir evenly, heat to 70 °C, and hold the reaction for 4 h. During the reaction, maintain the pH at 7 - 8 with sodium hydroxide solution;

[0060] (2) Distill off ethanol under reduced pressure, add 458 g of deionized water, 0.65 mol of acrylamide, 0.16 mol of [3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide, 0.08 mol of undecenoic acid, and 4.8 g of OP-10. Stir to dissolve, adjust the pH to 7 - 8 with sodium hydroxide, purge the reactor with nitrogen to displace the air in the reaction kettle, and continuously introduce nitrogen during the subsequent synthesis process;

[0061] (3) Add 30.4 g of initiator to the high-position dropping tank. The initiator contains 11 wt% of ammonium persulfate and 4 wt% of sodium bisulfite. Drop it into the reaction kettle. During the dropping process, the solution automatically heats up. Continue the reaction for 1 h, heat up to 70 °C, hold the reaction for 6 h, cool down to below 40 °C, and adjust the pH to 7 - 8 with sodium hydroxide;

[0062] (4) Dry and granulate the above-mentioned mixed solution to obtain polyacrylamide for enhanced oil recovery.

[0063] Example 6

[0064] (1) Purge the reactor with nitrogen for 8 min, then successively add 0.05 mol of laurylamine dipropylenediamine, 198 g of ethanol, and 0.105 mol of allyl chloride. Stir evenly, heat to 65 °C, and hold the reaction for 4 h. During the reaction, maintain the pH at 7 - 8 with sodium hydroxide solution;

[0065] (2) Distill off ethanol under reduced pressure, add 345 g of deionized water, 0.6 mol of acrylamide, 0.18 mol of [3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide, 0.08 mol of undecenoic acid, and 5.6 g of OP-10. Stir to dissolve, adjust the pH to 7 - 8 with sodium hydroxide, purge the reactor with nitrogen to displace the air in the reaction kettle, and continuously introduce nitrogen during the subsequent synthesis process;

[0066] (3) Add 41.2 g of initiator to the high-position dropping tank. The initiator contains 11 wt% of ammonium persulfate and 3 wt% of sodium bisulfite. Drop it into the reaction kettle. During the dropping process, the solution automatically heats up. Continue the reaction for 3 h, heat up to 62 °C, hold the reaction for 8 h, cool down to below 40 °C, and adjust the pH to 7 - 8 with sodium hydroxide;

[0067] (4) Dry and granulate the above-mentioned mixed solution to obtain polyacrylamide for enhanced oil recovery.

[0068] Example 7

[0069] (1) Purge the reactor with nitrogen for 8 min, then sequentially add 0.05 mol of laurylamine dipropylenediamine, 188 g of ethanol, and 0.1 mol of allyl chloride. Stir evenly, heat to 65 °C, and hold the reaction for 3 h. During the reaction, maintain the pH at 7 - 8 with sodium hydroxide solution.

[0070] (2) Distill off ethanol under reduced pressure, add 299 g of deionized water, 0.5 mol of acrylamide, 0.2 mol of [3-(methacrylamido)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide, 0.1 mol of undecylenic acid, and 6 g of OP-10. Stir to dissolve, adjust the pH to 7 - ⑧ with sodium hydroxide, purge the reactor with nitrogen to displace the air in the reaction kettle, and continuously introduce nitrogen during the subsequent synthesis process.

[0071] (3) Add 43 g of initiator to the high-level dropping tank. The initiator contains 11 wt% of ammonium persulfate and 3 wt% of sodium bisulfite. Drop it into the reaction kettle. During the dropping process, the solution automatically heats up. Continue the reaction for 4 h, heat up to 63 °C, hold the reaction for 6 h, cool down to below 40 °C, and adjust the pH to 7 - 8 with sodium hydroxide.

[0072] (4) Dry and granulate the above-mentioned mixed solution to obtain polyacrylamide for enhanced oil recovery.

[0073] Example 8 Measurement of Apparent Viscosity

[0074] Prepare a solution with a concentration of 1500 mg / L of the polyacrylamide for enhanced oil recovery (Examples 1 - 7) of the present invention with tap water, and measure the apparent viscosity with a Haake rheometer at 60 °C. Use the polyacrylamide for enhanced oil recovery of Shengli Chemical Co., Ltd. of Shengli Oilfield as a comparative example. The test results are shown in Table 1.

[0075] As can be seen from Table 1: The apparent viscosities of the polyacrylamide for enhanced oil recovery (Examples 1 - 7) of the present invention all reach 120 mPa·s or more at a concentration of 1500 mg / L under the condition of 60 °C, and the highest reaches 141 mPa·s (Example 7); while the apparent viscosity of the polyacrylamide for enhanced oil recovery of the comparative example, Shengli Chemical Co., Ltd. of Shengli Oilfield, is 35 mPa·s, which is significantly lower than that of the present invention.

[0076] Example 9 Determination of Viscosity Reduction Rate

[0077] The polyacrylamide for oil displacement of the present invention (Examples 1-7) was prepared into a 1000 mg / L solution with deionized water and preheated in a water bath at 75°C. The crude oil (viscosity 13200 mPa·s) from a certain heavy oil block in Shengli Oilfield was preheated in a water bath at 75°C. 30 g of each was taken and placed in a 100 ml stoppered graduated cylinder, and the water bath at 75°C was continued to heat for 0.5 h. The stoppered lid was tightly pressed by hand and shaken up and down 50-60 times, the viscosity was measured, and the viscosity reduction rate was calculated. The results are shown in Table 1.

[0078]

[0079] Where:

[0080] f —— Viscosity reduction rate, %;

[0081] μ 0 —— Initial viscosity of crude oil at 75°C, mPa·s;

[0082] μ —— Viscosity of crude oil after viscosity reduction, mPa·s.

[0083] Using the polyacrylamide for oil displacement of Shengli Chemical Co., Ltd. in Shengli Oilfield as a comparative example, the test results are shown in Table 1.

[0084] As can be seen from Table 1: The high-temperature resistant polyacrylamide for oil displacement of the present invention (Examples 1-7) has a good high-temperature viscosity reduction effect. At a concentration of 1000 mg / L at 75°C, the viscosity reduction rate of crude oil with a viscosity of 13200 mPa·s reaches over 98%, and the highest reaches 99.1% (Example 5); while for the comparative example of the polyacrylamide for oil displacement of Shengli Chemical Co., Ltd. in Shengli Oilfield, the crude oil does not separate layers, and the viscosity reduction effect is significantly lower than that of the present invention.

[0085] Example 10 Shear resistance test

[0086] The sample in Example 8 was continuously sheared for 2 h at 60°C and 170S -1 under the conditions, the apparent viscosity was measured, and the viscosity retention rate was calculated. Using the polyacrylamide for oil displacement of Shengli Chemical Co., Ltd. in Shengli Oilfield as a comparative example, the test results are shown in Table 1.

[0087] Table 1 Test results of apparent viscosity, viscosity reduction, and shear resistance

[0088]

[0089] As can be seen from Table 1: The polyacrylamide for oil displacement of the present invention (Examples 1-7) at 60°C and 170S -1Under the above conditions, continuous shearing for 2 h was carried out, and the viscosity retention rates all reached 91% or more, with the highest reaching 93.5% (Example 6); while the viscosity retention rate of the displacement polyacrylamide of Shengli Chemical Industry Co., Ltd. in the comparative example was 82.9%, which was significantly lower than that of the present invention.

[0090] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A preparation method of polyacrylamide for oil displacement, characterized in that, The specific steps of the preparation method are as follows: (1) Purge the reactor with nitrogen for 6 - 8 min. Then, add laurylamine dipropylenediamine, ethanol, and allyl chloride in sequence, stir evenly, heat for heat preservation reaction, and maintain the pH at 7 - 8 with sodium hydroxide solution during the reaction; (2) Distill off ethanol under reduced pressure. Add deionized water, acrylamide, [3-(methacrylamido)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide, undecylenic acid, and OP-10, stir to dissolve, adjust the pH to 7 - 8 with sodium hydroxide, purge the reactor with nitrogen to displace the air in the reaction kettle, and continuously introduce nitrogen during the subsequent synthesis process; (3) Add the initiator to the high-level dropping tank and drop it into the reaction kettle. During the dropping process, the solution automatically heats up. Continue the reaction for 1 - 4 h, heat up to 60 - 70 °C, keep the temperature for 2 - 8 h, cool down to below 40 °C, and adjust the pH to 7 - 8 with sodium hydroxide; (4) Dry and granulate the mixed solution to obtain polyacrylamide for enhanced oil recovery; The molar ratio of allyl chloride, acrylamide, [3-(methacrylamido)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide, undecylenic acid to laurylamine dipropylenediamine is 1.6 - 2.4:10 - 20:1 - 4:0.5 - 2:1; The molecular structural formula of the polyacrylamide for enhanced oil recovery is as follows: ， Wherein: o=2000-20000； m=20000-400000； n=2000-80000； p=1000-40000。 2. The preparation method of polyacrylamide for oil displacement according to claim 1, characterized in that, In step (1), the weight ratio of ethanol to laurylamine dipropylenediamine is 10 - 20:

1.

3. The preparation method of polyacrylamide for oil displacement according to claim 1, characterized in that, In step (1), the temperature for heat preservation reaction is 60 - 80 °C, and the time is 1 - 4 h.

4. The preparation method of polyacrylamide for oil displacement according to claim 1, characterized in that, In step (2), the weight ratio of deionized water, OP-10 to laurylamine dipropylenediamine is 20 - 40:0.2 - 0.4:

1.

5. The preparation method of a polyacrylamide for oil displacement according to claim 1, wherein, In step (3), the initiator is a mixed solution of persulfate and sodium bisulfite, wherein the concentration of persulfate is 10 - 12 wt%, the concentration of sodium bisulfite is 3 - 5 wt%, and the weight ratio of the initiator to laurylamine dipropylenediamine is 1 - 4:

1.

6. The preparation method of polyacrylamide for oil displacement according to claim 5, characterized in that, The persulfate is one of potassium persulfate, ammonium persulfate, and sodium persulfate.

7. A polyacrylamide for oil displacement, characterized in that, The molecular structural formula of the polyacrylamide is as follows: ， Wherein: o=2000-20000； m=20000-400000； n=2000-80000； p=1000-40000。 8. The polyacrylamide for oil displacement according to claim 7, characterized in that, The viscosity-average molecular weight of the polyacrylamide is 35,000,000 - 50,000,000.

9. The application of the polyacrylamide for enhanced oil recovery according to claim 7 in polymer flooding.

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