Polyacrylamide for oil displacement as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of tertiary oil recovery, and particularly relates to polyacrylamide for oil displacement and a preparation method and application thereof. The preparation method comprises the following steps: purging a reactor with nitrogen, sequentially adding lauryl amine dipropylidene diamine, ethanol and allyl chloride, uniformly stirring, heating, and carrying out a heat preservation reaction; adding deionized water, acrylamide, [3-(methacrylamido) propyl] dimethyl (3-thiopropyl) ammonium hydroxide, undecylenic acid and OP-10, and stirring for dissolving; adding an initiator into a high-position dropwise adding tank, dropwise adding the initiator into the reaction kettle, continuously reacting, heating, carrying out heat preservation reaction, and cooling to below 40 DEG C; and drying and granulating the mixed solution to obtain the polyacrylamide for oil displacement. The polyacrylamide for oil displacement has the characteristics of high apparent viscosity, good viscosity reduction effect and shear resistance.

Description

Technical Field

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

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

[0003] However, polyacrylamide is easily hydrolyzed in formation water and is sensitive to some ions in formation water, so the polymer viscosity will drop quickly. In addition, after the polymer solution is strongly sheared in the reservoir pores, its polymer molecular chains will deform and break, resulting in a rapid drop 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 displacement polymer, thereby affecting the oil recovery effect. Therefore, polyacrylamide with significant viscosity-enhancing effect, good resistance to high temperature and high salt, shear resistance, good thermal stability, and the ability to 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 and its application in oil production. The invention adopts a high temperature resistant hydrolysis copolymer to better solve the problem of poor hydrolysis stability of polyacrylamide under high temperature and high mineralization conditions in the prior art. It can be used in oil production in oil fields. However, the invention does not have a surfactant group in the molecular structure, and only has the function of ordinary polymer flooding, which cannot reduce the oil-water interfacial tension, cannot emulsify and reduce viscosity, and affects the recovery rate.

[0005] CN103739758A discloses a method for preparing polyacrylamide for oil fields, and 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 acid to adjust the pH value to 6-7, cool to 2-5°C, introduce nitrogen to drive out oxygen in the system, and when the oxygen content of the system is less than 0.001%, add an azo initiator, a complexing agent, a high-efficiency chain transfer agent, a reducing agent, and an oxidizing agent in sequence, seal the system after reaction, keep it warm in a water bath at 80°C for 1-2h, take out the colloid and grind it, add an inorganic base, hydrolyze it at 70-90°C for 1-2h, and finally dry and crush the colloid to obtain a high-resolution 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, and fully meets the standards for tertiary oil recovery in oil fields. However, the invention has a poor viscosity-increasing effect in highly mineralized reinjection water, which affects its effect. Summary of the invention

[0006] The present invention aims at the above-mentioned deficiencies of the prior art and provides a polyacrylamide for oil displacement and a preparation method and application thereof. 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-mentioned object, one of the objects of the present invention is to disclose a polyacrylamide for oil displacement, wherein the molecular structure of the polyacrylamide is as follows: , in: o=2000-20000; m = 20000-400000; n = 2000-80000; p=1000-40000.

[0008] In the present invention, preferably, the viscosity average molecular weight of the polyacrylamide is 35000000-50000000.

[0009] Another object of the present invention is to disclose a method for preparing the above-mentioned polyacrylamide for oil displacement, and the specific steps of the preparation method are as follows: (1) Purge the reactor with nitrogen for 6-8 minutes, add laurylamine dipropylene diamine, ethanol, and allyl chloride in sequence, stir evenly, heat and keep warm for reaction, and use sodium hydroxide solution to maintain pH 7-8 during the reaction; (2) Ethanol was distilled off under reduced pressure, and deionized water, acrylamide, [3-(methacrylamido)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, undecylenic acid, and OP-10 were added, stirred and dissolved, and the pH was adjusted to 7-8 with sodium hydroxide. The reactor was purged with nitrogen to replace the air in the reactor. Nitrogen was always introduced during the later synthesis process; (3) Add initiator to the high-position drop-adding tank and drip it into the reactor. During the dripping process, the solution automatically heats up and continues to react for 1-4 hours. Heat to 60-70°C and keep the temperature for 2-8 hours. Cool down to below 40°C and adjust the pH to 7-8 with sodium hydroxide. (4) Drying and granulating the mixed solution to obtain polyacrylamide for oil displacement.

[0010] In the present invention, preferably, the molar ratio of allyl chloride, acrylamide, [3-(methacrylamido)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, undecylenic acid and laurylamine dipropylene diamine is 1.6-2.4:10-20:1-4:0.5-2:1.

[0011] In the present invention, preferably, in step (1), the weight ratio of ethanol to laurylamine dipropylene diamine is 10-20:1.

[0012] In the present invention, preferably, in step (1), the heating and insulation reaction temperature is 60-80°C and the time is 1-4h.

[0013] In the present invention, preferably, in step (2), the weight ratio of deionized water, OP-10 and laurylamine dipropylene diamine is 20-40:0.2-0.4:1.

[0014] 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 10-12wt%, the concentration of sodium bisulfite is 3-5wt%, and the weight ratio of the initiator to laurylamine dipropylene diamine is 1-4:1.

[0015] Preferably, the persulfate is one of potassium persulfate, ammonium persulfate and sodium persulfate.

[0016] The equation for the synthetic reaction of polyacrylamide for oil displacement of the present invention is as follows:

[0017]

[0018]

[0019] The third object of the present invention is to disclose the application of the above polyacrylamide in polymer flooding.

[0020] The polyacrylamide for oil displacement of the present invention is a reticular polymer with acrylamide as the main body, has a higher viscosity, has a good profile control effect, and contains multiple lipophilic and hydrophilic groups. The lipophilic group is a polyethylene chain and a dodecyl group, wherein the dodecyl group is a flexible long-chain lipophilic group, which can penetrate into the crude oil and fully combine with the crude oil; the hydrophilic group has a carboxyl group, a sulfonic acid group, and a quaternary ammonium salt, which can reduce the oil-water interfacial tension, emulsify the crude oil to reduce the viscosity of the crude oil, and transfer the peeled crude oil to the water phase, especially undecanoic acid belongs to a flexible long-chain hydrophilic group, which can better enter the water phase, so that the emulsified crude oil is mined with the water phase; the molecule also contains a quaternary ammonium salt, which has a bactericidal effect, and in the oil displacement process, especially in low-temperature oil reservoirs, it can prevent the destruction of the polymer by microorganisms, and assist in improving the crude oil recovery rate.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The polyacrylamide for oil displacement of 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 above; (2) The high temperature resistant polyacrylamide for oil recovery of the present invention has a good high temperature viscosity reduction effect. The viscosity reduction rate of 1000 mg / L of crude oil with a viscosity of 13200 mPa·s at 75°C is more than 98%; (3) The polyacrylamide for oil displacement of the present invention has shear resistance. After 2 hours of shearing, the viscosity retention rate reaches 91% or more. DETAILED DESCRIPTION

[0022] 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.

[0023] The technical solution of the present invention is further described below in conjunction with specific embodiments:

[0024] Example 1 (1) Purge the reactor with nitrogen for 6 minutes, add 0.05 mol of laurylamine dipropylene diamine, 299 g of ethanol, and 0.12 mol of allyl chloride in sequence, stir evenly, heat to 60°C, and keep the temperature for 4 hours. During the reaction, use sodium hydroxide solution to maintain the pH at 7-8; (2) Ethanol was distilled off under reduced pressure, and 598 g of deionized water, 1 mol of acrylamide, 0.05 mol of [3-(methacrylamido)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, 0.025 mol of undecylenic acid, and 3 g of OP-10 were added, stirred and dissolved, and the pH was adjusted to 7-8 with sodium hydroxide. The reactor was purged with nitrogen to replace the air in the reactor. Nitrogen was always introduced during the later synthesis process; (3) Add 59.8g of initiator containing 10wt% potassium persulfate and 3wt% sodium bisulfite into the high-position dropping tank and drip it into the reactor. During the dropping process, the solution automatically heats up and continues to react for 1h. The temperature is then raised to 70°C and kept at this temperature for 2h. The temperature is then lowered to below 40°C and the pH is adjusted to 7-8 with sodium hydroxide. (4) Drying and granulating the mixed solution to obtain polyacrylamide for oil displacement.

[0025] Example 2 (1) Purge the reactor with nitrogen for 6 minutes, add 0.05 mol of laurylamine dipropylene diamine, 149.5 g of ethanol, and 0.08 mol of allyl chloride in sequence, stir evenly, heat to 65°C, and keep the temperature for 4 hours. During the reaction, use sodium hydroxide solution to maintain the pH at 7-8; (2) Ethanol was distilled off under reduced pressure, and 544 g of deionized water, 0.9 mol of acrylamide, 0.08 mol of [3-(methacrylamido)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, 0.035 mol of undecylenic acid, and 3.4 g of OP-10 were added, stirred and dissolved, and the pH was adjusted to 7-8 with sodium hydroxide. The reactor was purged with nitrogen to replace the air in the reactor. Nitrogen was always introduced during the later synthesis process; (3) 50.3 g of initiator containing 10 wt% potassium persulfate and 3 wt% sodium bisulfite was added to the high-position drop-adding tank and dripped into the reactor. During the dripping process, the solution automatically heated up and continued to react for 4 h. The temperature was heated to 60 ° C and kept at this temperature for 8 h. The temperature was then lowered to below 40 ° C and the pH was adjusted to 7-8 with sodium hydroxide. (4) Drying and granulating the mixed solution to obtain polyacrylamide for oil displacement.

[0026] Example 3 (1) Purge the reactor with nitrogen for 6 min, add 0.05 mol of laurylamine dipropylene diamine, 243 g of ethanol, and 0.09 mol of allyl chloride in sequence, stir evenly, heat to 70 °C, and keep the temperature for 1 h. During the reaction, use sodium hydroxide solution to maintain the pH at 7-8; (2) Ethanol was distilled off under reduced pressure, and 504 g of deionized water, 0.8 mol of acrylamide, 0.1 mol of [3-(methacrylamido)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, 0.04 mol of undecylenic acid, and 3.8 g of OP-10 were added, stirred and dissolved, and the pH was adjusted to 7-8 with sodium hydroxide. The reactor was purged with nitrogen to replace the air in the reactor. Nitrogen was always introduced during the later synthesis process; (3) 14.95 g of initiator containing 12 wt% sodium persulfate and 5 wt% sodium bisulfite was added to the high-position dropping tank and dripped into the reactor. During the dripping process, the solution automatically heated up and continued to react for 2 h. The temperature was heated to 65 ° C and kept for 4 h. The temperature was lowered to below 40 ° C and the pH was adjusted to 7-8 with sodium hydroxide. (4) Drying and granulating the mixed solution to obtain polyacrylamide for oil displacement.

[0027] Example 4 (1) Purge the reactor with nitrogen for 7 minutes, add 0.05 mol of laurylamine dipropylene diamine, 276 g of ethanol, and 0.11 mol of allyl chloride in sequence, stir evenly, heat to 80°C, and keep the temperature for 2 hours. During the reaction, use sodium hydroxide solution to maintain the pH at 7-8; (2) Ethanol was distilled off under reduced pressure, and 436 g of deionized water, 0.7 mol of acrylamide, 0.14 mol of [3-(methacrylamido)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, 0.05 mol of undecylenic acid, and 4 g of OP-10 were added, stirred and dissolved, and the pH was adjusted to 7-8 with sodium hydroxide. The reactor was purged with nitrogen to replace the air in the reactor. Nitrogen was always introduced during the later synthesis process; (3) 21.7 g of initiator containing 12 wt% sodium persulfate and 4 wt% sodium bisulfite was added to the high-position dropping tank and dripped into the reactor. During the dripping process, the solution automatically heated up and continued to react for 3 h. The temperature was heated to 60 ° C and kept for 8 h. The temperature was lowered to below 40 ° C and the pH was adjusted to 7-8 with sodium hydroxide. (4) Drying and granulating the mixed solution to obtain polyacrylamide for oil displacement.

[0028] Example 5 (1) Purge the reactor with nitrogen for 7 minutes, add 0.05 mol of laurylamine dipropylene diamine, 204 g of ethanol, and 0.095 mol of allyl chloride in sequence, stir evenly, heat to 70°C, and keep the temperature for 4 hours. During the reaction, use sodium hydroxide solution to maintain the pH at 7-8; (2) Ethanol was distilled off under reduced pressure, and 458 g of deionized water, 0.65 mol of acrylamide, 0.16 mol of [3-(methacrylamido)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, 0.08 mol of undecylenic acid, and 4.8 g of OP-10 were added, stirred and dissolved, and the pH was adjusted to 7-8 with sodium hydroxide. The reactor was purged with nitrogen to replace the air in the reactor. Nitrogen was always introduced during the later synthesis process; (3) 30.4 g of initiator containing 11 wt% ammonium persulfate and 4 wt% sodium bisulfite was added to the high-position dropping tank and dripped into the reactor. During the dropping process, the solution automatically heated up and continued to react for 1 hour. The temperature was heated to 70°C and kept for 6 hours. The temperature was then lowered to below 40°C and the pH was adjusted to 7-8 with sodium hydroxide. (4) Drying and granulating the mixed solution to obtain polyacrylamide for oil displacement.

[0029] Example 6 (1) Purge the reactor with nitrogen for 8 minutes, add 0.05 mol of laurylamine dipropylene diamine, 198 g of ethanol, and 0.105 mol of allyl chloride in sequence, stir evenly, heat to 65°C, and keep the temperature for 4 hours. During the reaction, use sodium hydroxide solution to maintain the pH at 7-8; (2) Ethanol was distilled off under reduced pressure, and 345 g of deionized water, 0.6 mol of acrylamide, 0.18 mol of [3-(methacrylamido)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, 0.08 mol of undecylenic acid, and 5.6 g of OP-10 were added, stirred and dissolved, and the pH was adjusted to 7-8 with sodium hydroxide. The reactor was purged with nitrogen to replace the air in the reactor. Nitrogen was always introduced during the later synthesis process; (3) 41.2 g of initiator containing 11 wt% ammonium persulfate and 3 wt% sodium bisulfite was added to the high-position drop-adding tank and dripped into the reactor. During the dripping process, the solution automatically heated up and continued to react for 3 h. The temperature was heated to 62 °C and kept at this temperature for 8 h. The temperature was then lowered to below 40 °C and the pH was adjusted to 7-8 with sodium hydroxide. (4) Drying and granulating the mixed solution to obtain polyacrylamide for oil displacement.

[0030] Example 7 (1) Purge the reactor with nitrogen for 8 minutes, add 0.05 mol of laurylamine dipropylene diamine, 188 g of ethanol, and 0.1 mol of allyl chloride in sequence, stir evenly, heat to 65°C, and keep the temperature for 3 hours. During the reaction, use sodium hydroxide solution to maintain the pH at 7-8; (2) Ethanol was distilled off under reduced pressure, and 299 g of deionized water, 0.5 mol of acrylamide, 0.2 mol of [3-(methacrylamido)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, 0.1 mol of undecylenic acid, and 6 g of OP-10 were added, stirred and dissolved, and the pH was adjusted to 7-8 with sodium hydroxide. The reactor was purged with nitrogen to replace the air in the reactor. Nitrogen was always introduced during the later synthesis process; (3) 43 g of initiator containing 11 wt% ammonium persulfate and 3 wt% sodium bisulfite was added to the high-position drop-adding tank and dripped into the reactor. During the dripping process, the solution automatically heated up and continued to react for 4 h. The temperature was heated to 63 ° C and kept for 6 h. The temperature was then cooled to below 40 ° C and the pH was adjusted to 7-8 with sodium hydroxide. (4) Drying and granulating the mixed solution to obtain polyacrylamide for oil displacement.

[0031] Example 8 Test of apparent viscosity The polyacrylamide for oil displacement (Examples 1-7) of the present invention was prepared into a solution with a concentration of 1500 mg / L with tap water, and the apparent viscosity was tested with a Haake rheometer at 60° C. The polyacrylamide for oil displacement produced by Shengli Oilfield Shengli Chemical Co., Ltd. was used as a comparative example, and the test results are shown in Table 1.

[0032] It can be seen from Table 1 that the apparent viscosity of the polyacrylamide for oil displacement of the present invention (Examples 1-7) at a concentration of 1500 mg / L at 60°C is 120 mPa·s or above, and the highest is 141 mPa·s (Example 7); while the apparent viscosity of the polyacrylamide for oil displacement of the comparative example Shengli Oilfield Shengli Chemical Co., Ltd. is 35 mPa·s, which is significantly lower than that of the present invention.

[0033] Example 9 Determination of viscosity reduction The polyacrylamide for oil displacement (Examples 1-7) of the present invention was prepared into a 1000 mg / L solution with deionized water, and preheated in a water bath at 75°C. Crude oil (viscosity of 13200 mPa·s) from a heavy oil block of Shengli Oilfield was preheated in a water bath at 75°C. 30 g of each was placed in a 100 ml stoppered measuring cylinder, and continued to be heated in a water bath at 75°C for 0.5 h. The stoppered cover was pressed tightly by hand and oscillated up and down 50-60 times to test the viscosity and calculate the viscosity reduction rate. The results are shown in Table 1.

[0034]

[0035] Where: f ——Viscosity reduction rate, %; m 0 ——Initial viscosity of crude oil at 75℃, mPa·s; m ——Viscosity of crude oil after viscosity reduction, mPa·s.

[0036] The oil displacement polyacrylamide produced by Shengli Oilfield Shengli Chemical Co., Ltd. was used as a comparative example, and the test results are shown in Table 1.

[0037] It can be seen from Table 1 that the high temperature resistant polyacrylamide for oil recovery (Examples 1-7) of the present invention has a good high temperature viscosity reduction effect. The viscosity reduction rate of 1000 mg / L concentration for crude oil with a viscosity of 13200 mPa·s at 75°C is more than 98%, and the highest is 99.1% (Example 5). However, the oil recovery polyacrylamide of Shengli Oilfield Shengli Chemical Co., Ltd. in the comparative example does not stratify the crude oil, and the viscosity reduction effect is significantly lower than that of the present invention.

[0038] Example 10 Shear resistance test The sample in Example 8 was heated at 60°C and 170S -1The apparent viscosity was tested and the viscosity retention rate was calculated under the condition of continuous shearing for 2 hours. The oil displacement polyacrylamide of Shengli Oilfield Shengli Chemical Co., Ltd. was used as a comparative example, and the test results are shown in Table 1.

[0039] Table 1 Test results of apparent viscosity, viscosity reduction and shear resistance

[0040] It can be seen from Table 1 that the polyacrylamide for oil displacement of the present invention (Examples 1-7) at 60°C and 170S -1 Under the conditions of continuous shearing for 2 hours, the viscosity retention rate reached 91% and above, with the highest reaching 93.5% (Example 6); while the viscosity retention rate of the oil-displacing polyacrylamide of Shengli Oilfield Shengli Chemical Co., Ltd. in the comparative example was 82.9%, which was significantly lower than that of the present invention.

[0041] 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 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 minutes, add laurylamine dipropylene diamine, ethanol, and allyl chloride in sequence, stir evenly, heat and keep warm for reaction, and use sodium hydroxide solution to maintain pH 7-8 during the reaction; (2) Ethanol was distilled off under reduced pressure, and deionized water, acrylamide, [3-(methacrylamido)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, undecylenic acid, and OP-10 were added, stirred and dissolved, and the pH was adjusted to 7-8 with sodium hydroxide. The reactor was purged with nitrogen to replace the air in the reactor. Nitrogen was always introduced during the later synthesis process; (3) Add initiator to the high-position drop-adding tank and drip it into the reactor. During the dripping process, the solution automatically heats up and continues to react for 1-4 hours. Heat to 60-70°C and keep the temperature for 2-8 hours. Cool down to below 40°C and adjust the pH to 7-8 with sodium hydroxide. (4) drying and granulating the mixed solution to obtain polyacrylamide for oil displacement; The molar ratio of allyl chloride, acrylamide, [3-(methacrylamido)propyl]dimethyl(3-thiopropyl)ammonium hydroxide, undecylenic acid and laurylamine dipropylene diamine is 1.6-2.4:10-20:1-4:0.5-2:1; The molecular structure of the polyacrylamide for oil displacement is as follows: ， in: o=2000-20000； m=20000-400000； n=2000-80000； p=1000-40000。 2. The method for preparing a polyacrylamide for oil displacement according to claim 1, characterized in that: In step (1), the weight ratio of ethanol to laurylamine dipropylene diamine is 10-20:

1.

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

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

1.

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

1.

6. The method for preparing 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 structure of polyacrylamide is as follows: ， in: 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 35000000-50000000.

9. Use of the polyacrylamide for oil recovery according to claim 7 in polymer oil recovery.

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