Low-molecular-weight oil displacement polymer suitable for low-permeability reservoir and preparation method of low-molecular-weight oil displacement polymer

Abstract

The invention belongs to the technical field of polymer modification, and relates to a low molecular weight oil displacement polymer suitable for a low permeability reservoir, which is prepared from the following raw materials by mass: 10-20 parts of an organic solvent A; 1-5 parts of an organic solvent B; 100 to 150 parts of a monomer C with a propenyl group; 50 to 100 parts of monomer D with an ammonium group; 1-10 parts of a monomer E; 1-5 parts of a dispersant F; and 0.01 to 0.05 part of an initiator G. The preparation method comprises the following steps: carrying out free radical reaction on the three monomers to obtain the polymer; adding dry ice while adding the monomer to form a microbubble environment; performing low-temperature initiation in a micro-bubble environment, then introducing nitrogen, forming a micro-pressure condition, placing in a water bath, and performing micro-bubble low-temperature micro-pressure reaction to weaken the difference value of reactivity among all reaction monomers, so that the reaction activity of all the monomers is kept in an approximate range, and the polymer with the physical structure suitable for low-molecular-weight oil displacement of a low-permeability reservoir is synthesized.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer modification, and in particular relates to a low-molecular-weight oil-displacing polymer suitable for low-permeability reservoirs and a preparation method thereof. Background Art

[0002] The polymers used for chemical flooding of low permeability reservoirs are quite different from those used for chemical flooding of medium and high permeability reservoirs. The polymer viscosity average molecular weight is related to injectivity and permeability, so a lower polymer viscosity average molecular weight (5 million to 8 million) is required. The Jurassic low permeability reservoir has difficulties such as low permeability and high mineralization of formation water and injection water. The polymer needs to have solubility, injectability, salt resistance, and shear resistance. In view of the characteristics of the Changqing reservoir, the chemical flooding method of polymer-surfactant binary flooding requires the compatibility of polymer and betaine-type surfactant.

[0003] However, there is a lack of polymer products with all of the above functions on the market. The current ordinary polymers cannot simultaneously meet the properties of molecular weight, solubility, injectability, salt resistance, shear resistance, etc. For example, SY / T5862-2020 "Technical Requirements for Polymers for Oil Displacement" requires an intrinsic viscosity of ≥2500ml / g, calculated as a viscosity-average molecular weight of ≥14 million, a dissolution time of ≤120min, a filtration factor of ≤2.0, an apparent viscosity of ≥12.5mPa·s, and a shear viscosity retention rate of ≥80%. Generally speaking, the larger the molecular weight, the greater the apparent viscosity to be achieved.

[0004] Among the currently disclosed patents, there is no patent specifically for low molecular weight polymers used for oil recovery in low permeability reservoirs. Summary of the invention

[0005] The purpose of the present invention is to provide a low molecular weight oil recovery polymer suitable for low permeability reservoirs and a preparation method thereof, thereby solving the problem that ordinary polymers are not suitable for low permeability reservoirs.

[0006] The present invention is achieved through the following technical solutions:

[0007] A low molecular weight oil recovery polymer suitable for low permeability reservoirs, having the structural formula:

[0008]

[0009] Further, it is prepared from the following raw materials by weight:

[0010] 10-20 parts of organic solvent A;

[0011] Organic solvent B 1-5 parts;

[0012] 100-150 parts of monomer C with acrylic group;

[0013] 50-100 parts of monomer D having an ammonium group;

[0014] 1-10 parts of monomer E; monomer E is an ester compound;

[0015] Dispersant F 1-5 parts;

[0016] Initiator G 0.01-0.05 part;

[0017] 300 parts of water.

[0018] Furthermore, the organic solvent A is selected from at least one of xylene, tetrachloroethylene, kerosene, diesel, paraffin, ethanol and white oil.

[0019] Furthermore, the organic solvent B is selected from at least one of sorbitan stearate, alkylphenol polyoxyethylene ether, Tween 80, emulsifier A-7, No. 26 white mineral oil, white vaseline, and sorbitol.

[0020] Furthermore, the monomer C is selected from at least one of acrylic acid, methacrylic acid, acrylamide, dimethyldipropylenebenzenesulfonic acid, maleic anhydride and dimethyldipropylenebenzenesulfonate.

[0021] Furthermore, the monomer D is selected from at least one of dimethyldiallylammonium chloride, dimethylaminoethyl methacrylate quaternary ammonium salt, dimethylaminoethyl methacrylate methyl chloride salt, and dimethylaminopropyl acrylamide.

[0022] Furthermore, the monomer E is selected from at least one of methyl acrylate, ethyl acrylate, methyl 2-methacrylate, ethyl 2-methacrylate, hexadecyl acrylate, and fluorocarbon-modified acrylate.

[0023] Further, the dispersant F is selected from at least one of silicate, sodium tripolyphosphate, sodium hexametaphosphate, ammonium lauryl sulfate, methyl amyl alcohol, fatty acid polyglycol ester, and OP-10;

[0024] The initiator G is selected from at least one of hydrogen peroxide, potassium persulfate, sodium persulfate, ammonium persulfate, sodium sulfite, sodium bisulfite, cerium ammonium nitrate, benzoyl peroxide, azobisisobutylamidine hydrochloride, and azobisisobutylimidazoline hydrochloride.

[0025] The present invention also discloses a method for preparing a low molecular weight oil displacement polymer suitable for low permeability reservoirs, comprising the following steps:

[0026] (1) According to the mass percentage, prepare the following raw materials:

[0027] Organic solvent A 10-20 parts

[0028] Organic solvent B 1-5 parts;

[0029] 100-150 parts of monomer C with acrylic group;

[0030] 50-100 parts of monomer D having an ammonium group;

[0031] 1-10 parts of monomer E; monomer E is an ester compound;

[0032] Dispersant F 1-5 parts;

[0033] Initiator G 0.01-0.05 part;

[0034] 300 parts water;

[0035] (2) mixing organic solvent A, organic solvent B and water, maintaining the temperature at 10° C. to 15° C. and stirring to obtain a mixed solution;

[0036] (3) adding dry ice, monomer C, monomer D, and monomer E to the mixed solution while stirring, and stirring until the solution is uniform to obtain a uniform solution;

[0037] (4) The overall temperature of the homogeneous solution is reduced to below zero in a microbubble environment, and an initiator G is added dropwise to the homogeneous solution. Meanwhile, a dispersant F is added by nitrogen flow. The solution is sealed and reacted in a constant temperature water bath at 50°C-80°C for 4-8 hours. The solution is then formed into granules, dried, and crushed to obtain a low molecular weight oil recovery polymer suitable for low permeability reservoirs.

[0038] Furthermore, in step (4), the dripping time of the initiator is controlled within 30 minutes;

[0039] After sealing, a micro-pressure condition is formed and the mixture is placed in a 50-80°C water bath to react for 4-8 hours.

[0040] Compared with the prior art, the present invention has the following beneficial technical effects:

[0041] The present invention discloses a low molecular weight oil displacement polymer suitable for low permeability reservoirs, wherein the structural formula of the polymer contains a sulfonic acid group, which is a polar group, so that the polymer can still maintain a certain body structure under the condition of high mineralization, and has good salt resistance, and at the same time affects the amide group to form intramolecular and intermolecular hydrogen bonds, and has excellent solubility. The polar group reaches a balance with the monovalent and divalent cations in the formation water, and the molecular structure stretches to form a supramolecular aggregate with a weaker force. Under the influence of shear force, the polymer has a significant single molecule structure and has better injectability. When the external force is weakened, the polymer has a certain aggregation and entanglement performance, increases the viscosity of the system, and has better shear resistance. The polymer and the surfactant for binary flooding show better compatibility and thickening effect, and are more suitable for the use characteristics of high salt and low permeability in low permeability reservoirs, and polymer-surface binary flooding in some areas.

[0042] It can not only maintain a high viscosity in highly mineralized water, but its low molecular weight structure can also ensure that it maintains a low hydraulic radius when passing through the low permeability channel, allowing it to be smoothly injected. After passing through the low permeability channel, it can be aggregated into a supramolecular structure again, with excellent shear resistance. In the construction of polymer-surfactant binary flooding, it has a good compatibility and thickening effect with the surfactant, which is beneficial to the optimized application of the binary system, and can be better used in polymer-surfactant binary flooding operations in low permeability reservoirs, reducing the comprehensive water content and improving the recovery rate.

[0043] The invention discloses a method for preparing a low-molecular-weight oil-displacing polymer suitable for low-permeability reservoirs. The method comprises the following steps: three monomers are reacted to obtain a polymer through free radical reaction; dry ice is added simultaneously when the monomers are added to form a microbubble environment; low-temperature initiation is performed in the microbubble environment, and nitrogen is then introduced to form a micropressure condition; the polymer is placed in a water bath at 50-80°C for reaction for 4-8 hours; and the difference in the reactivity ratios between the reaction monomers is weakened through the microbubble low-temperature and micropressure reaction, so that the reaction activities of the monomers in a certain ratio are kept in a close range, thereby synthesizing a low-molecular-weight oil-displacing polymer suitable for low-permeability reservoirs. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the present invention clearer, the following is further described in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the embodiments described are only part of the embodiments of the present invention, rather than all the embodiments.

[0045] It should be noted that the terms "comprises", "includes" or any other variations are intended to cover non-exclusive inclusion, so that a process, element, method, article or equipment that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to the process, element, method, article or equipment.

[0046] The present invention discloses a low molecular weight oil displacement polymer suitable for low permeability reservoirs, and the structural formula thereof is:

[0047]

[0048] The product is prepared from the following raw materials by weight:

[0049] Organic solvent A: at least one of xylene, tetrachloroethylene, kerosene, diesel, paraffin and white oil is selected, and the mass consumption is 10-20 parts.

[0050] Organic solvent B: at least one of sorbitan stearate, alkylphenol polyoxyethylene ether, Tween 80, emulsifier A-7, No. 26 white mineral oil, white vaseline, and sorbitol is selected, and the mass consumption is 1-5 parts.

[0051] Monomer C: at least one of acrylic acid, methacrylic acid, acrylamide, dimethyldipropylenebenzenesulfonic acid, maleic anhydride, and dimethyldipropylenebenzenesulfonate is selected, and the weight consumption is 100-150 parts.

[0052] Monomer D: at least one of dimethyldiallylammonium chloride, dimethylaminoethyl methacrylate quaternary ammonium salt, dimethylaminoethyl methacrylate methyl chloride salt, and dimethylaminopropyl acrylamide is selected, and the weight consumption is 50-100 parts.

[0053] Monomer E: at least one of methyl acrylate, ethyl acrylate, methyl 2-methacrylate and ethyl 2-methacrylate, hexadecyl acrylate and fluorocarbon modified acrylate is selected, and the weight consumption is 1-10 parts.

[0054] Dispersant F: at least one of silicate, sodium tripolyphosphate, sodium hexametaphosphate, ammonium lauryl sulfate, methylpentanol, fatty acid polyglycol and OP-10 is selected, and the weight consumption is 1-5 parts.

[0055] Initiator G: at least one of hydrogen peroxide, potassium persulfate, sodium persulfate, ammonium persulfate, sodium sulfite, sodium bisulfite, cerium ammonium nitrate, benzoyl peroxide, azobisisobutylamidine hydrochloride, and azobisisobutylimidazoline hydrochloride is selected, and the mass consumption is 0.01-0.05 parts.

[0056] The mass consumption of water is 300 parts.

[0057] The chemical reaction process steps are:

[0058] According to the weight ratio of the above chemical reactants, organic solvent A, organic solvent B and water are added to a three-necked flask, the temperature is kept constant at 10°C-15°C, and after strong stirring for 10-20 minutes, dry ice, monomer C, monomer D and monomer E are added while stirring until the solution is uniform to obtain a uniform solution;

[0059] The overall temperature of the uniform solution is lowered to below zero in a microbubble environment, and initiator G is added dropwise to the uniform solution after nitrogen is passed through it. Dispersant F is also added while nitrogen is passed through it. The solution is sealed and reacted in a constant temperature water bath at 50°C-80°C for 4-8 hours to form colloid particles, which are then dried and crushed to obtain a powdery product.

[0060] The water used is distilled water with a conductivity of less than 5, and its total mass consumption accounts for 300 parts.

[0061] During the stirring and dissolving process, the temperature is controlled not to exceed 50° C., and the time for adding monomer C and monomer D is controlled within 30-120 minutes.

[0062] The features and performances of the present invention are further described in detail below in conjunction with the embodiments.

[0063] Example 1

[0064] As shown in Table 1, in a polymerization reaction vessel equipped with high-speed stirring and nitrogen-filled sealed vessel, 300 parts of water, 15 parts of white oil, and 2 parts of sorbitan stearate were added, the temperature was kept constant at 10° C., and after strong stirring for 10 minutes, a mixed solution was obtained under stirring;

[0065] Add dry ice, 150 parts of acrylamide, 125 parts of dimethylaminoethyl methacrylate methyl chloride, and 1 part of hexadecyl acrylate to the mixed solution under stirring, and stir until the solution is uniform to obtain a uniform solution;

[0066] In a microbubble environment, the overall temperature is lowered to below zero, 0.01 parts of ammonium persulfate (0.5% aqueous solution) are added dropwise, and 1 part of methyl amyl alcohol is added through nitrogen. The mixture is sealed and reacted in a constant temperature water bath at 50°C for 4 hours to form colloid particles. After drying and crushing, a low-molecular-weight oil displacement polymer suitable for low-permeability reservoirs is obtained.

[0067] As shown in Table 2, the low molecular weight oil recovery polymer suitable for low permeability reservoirs prepared in this embodiment has a molecular weight of 8.21 million, a filtration factor of 1.3, an apparent viscosity of 43.2 mPa·s, a shear viscosity retention rate of 92.2%, an injection pressure of 3.8 MPa, a resistance coefficient of 19, and a residual resistance coefficient of 3.

[0068] Example 2

[0069] In a polymerization reactor equipped with high-speed stirring and nitrogen-filled sealed vessel, 300 parts of water, 5 parts of tetrachloroethylene, 8 parts of paraffin, and 1 part of Tween 80 were added, the temperature was kept constant at 12°C, and after strong stirring for 20 minutes, a mixed solution was obtained under stirring;

[0070] Add dry ice, 130 parts of acrylamide, 18 parts of dimethyldiallylbenzenesulfonic acid, 50 parts of dimethyldiallylammonium chloride, 1 part of methyl 2-methacrylate and 1 part of ethyl 2-methacrylate to the mixed solution under stirring, and stir until the solution is uniform to obtain a uniform solution;

[0071] The overall temperature of the uniform solution was lowered to below zero in a microbubble environment. After nitrogen was passed through for 5 minutes, 0.01 parts of potassium persulfate, 0.01 parts of sodium bisulfite and 0.01 parts of azobis(isobutylene)imidazoline hydrochloride were added dropwise. At the same time, 1 part of dodecyl ammonium sulfate was added through nitrogen. The solution was sealed and reacted in a constant temperature water bath at 65°C for 6 hours to form colloid particles. After drying and crushing, a low molecular weight oil displacement polymer suitable for low permeability reservoirs was obtained.

[0072] As shown in Table 2, the low molecular weight oil recovery polymer suitable for low permeability reservoirs prepared in this embodiment has a molecular weight of 6.92 million, a filtration factor of 1.2, an apparent viscosity of 39.8 mPa·s, a shear viscosity retention rate of 91.4%, an injection pressure of 3.6 MPa, a resistance coefficient of 17.8, and a residual resistance coefficient of 4.

[0073] Example 3

[0074] In a polymerization reaction vessel equipped with high-speed stirring and nitrogen-filled sealed vessel, 300 parts of water, 15 parts of white oil, and 1 part of sorbitol were added, the temperature was kept constant at 15°C, and after strong stirring for 20 minutes, a mixed solution was obtained under stirring;

[0075] Add dry ice, 5 parts of acrylic acid, 130 parts of acrylamide, 15 parts of dimethyldipropylenebenzenesulfonic acid, 50 parts of dimethylaminoethyl methacrylate quaternary ammonium salt, 1 part of dimethylaminopropyl acrylamide, and 5 parts of hexadecyl acrylate to the mixed solution under stirring, and stir until the solution is uniform.

[0076] 0.02 parts of ammonium persulfate and 0.01 parts of sodium bisulfite were added dropwise, and 5 parts of OP-10 were added through nitrogen. The mixture was sealed and reacted in a constant temperature water bath at 60°C for 6 hours to form granules. After drying and crushing, a low molecular weight oil recovery polymer suitable for low permeability reservoirs was obtained.

[0077] As shown in Table 2, the low molecular weight oil recovery polymer suitable for low permeability reservoirs prepared in Example 3 has a molecular weight of 7.89 million, a filtration factor of 1.1, an apparent viscosity of 40.7 mPa·s, a shear viscosity retention rate of 91.8%, an injection pressure of 3.8 MPa, a resistance coefficient of 16.5, and a residual resistance coefficient of 3.

[0078] Example 4

[0079] As shown in Table 1, in a polymerization reaction vessel equipped with high-speed stirring and nitrogen-filled sealed vessel, 300 parts of water, 5 parts of kerosene, 15 parts of white oil, and 5 parts of alkylphenol polyoxyethylene ether were added, the temperature was kept constant at 15° C., and after strong stirring for 10 minutes, a mixed solution was obtained under stirring;

[0080] Add dry ice, 10 parts of acrylic acid, 100 parts of acrylamide, 30 parts of dimethyldiallylbenzenesulfonate, 10 parts of dimethyldiallylammonium chloride, 40 parts of dimethylaminopropylacrylamide, and 3 parts of hexadecyl acrylate to the mixed solution under stirring, and stir until the solution is uniform to obtain a uniform solution;

[0081] The overall temperature of the uniform solution was lowered to below zero in a microbubble environment, 0.05 parts of cerium ammonium nitrate was added dropwise, and 1 part of dodecyl ammonium sulfate was added through nitrogen. The solution was sealed and reacted in a constant temperature water bath at 50°C for 4 hours to form granules. After drying and crushing, a low molecular weight oil recovery polymer suitable for low permeability reservoirs was obtained.

[0082] As shown in Table 2, the low molecular weight oil recovery polymer suitable for low permeability reservoirs prepared in Example 4 has a molecular weight of 6.42 million, a filtration factor of 1.2, an apparent viscosity of 42.5 mPa·s, a shear viscosity retention rate of 92.7%, an injection pressure of 3.7 MPa, a resistance coefficient of 12, and a residual resistance coefficient of 3.

[0083] Example 5

[0084] In a polymerization reaction vessel equipped with high-speed stirring and nitrogen-filled sealed vessel, 300 parts of water, 1 part of xylene, 10 parts of white oil, 5 parts of paraffin, and 1 part of Tween 80 were added, the temperature was kept constant at 13°C, and after strong stirring for 20 minutes, a mixed solution was obtained under stirring;

[0085] Add dry ice, 20 parts of methacrylic acid, 110 parts of acrylamide, 15 parts of dimethyldiallylbenzenesulfonic acid, 40 parts of dimethyldiallylammonium chloride, 40 parts of dimethylaminopropylacrylamide, and 1 part of methyl acrylate to the mixed solution under stirring, and stir until the solution is uniform;

[0086] The overall temperature of the uniform solution was lowered to below zero in a microbubble environment. After nitrogen was passed through for 5 minutes, 0.03 parts of ammonium cerium nitrate and 0.02 parts of azobisisobutylamidine hydrochloride were added dropwise. At the same time, 1 part of fatty acid poly(hexanediol) was added through nitrogen. The solution was sealed and reacted in a constant temperature water bath at 65°C for 6 hours to form gel particles. After drying and crushing, a low molecular weight oil displacement polymer suitable for low permeability reservoirs was obtained.

[0087] As shown in Table 2, the low molecular weight oil recovery polymer suitable for low permeability reservoirs prepared in Example 5 has a molecular weight of 6.15 million, a filtration factor of 1.3, an apparent viscosity of 45.7 mPa·s, a shear viscosity retention rate of 94.7%, an injection pressure of 3.8 MPa, a resistance coefficient of 14, and a residual resistance coefficient of 3.

[0088] Example 6

[0089] In a polymerization reaction vessel equipped with high-speed stirring and nitrogen-filled sealed vessel, 300 parts of water, 20 parts of white oil, 1 part of sorbitan stearate, and 1 part of Tween 80 were added, the temperature was kept constant at 10°C, and after strong stirring for 20 minutes, a mixed solution was obtained under stirring;

[0090] Add dry ice, 10 parts of acrylic acid, 120 parts of acrylamide, 10 parts of dimethyldipropylenebenzenesulfonate, 50 parts of dimethylaminoethyl methacrylate quaternary ammonium salt, 10 parts of dimethylaminopropyl acrylamide, 1 part of ethyl acrylate, and 5 parts of hexadecyl acrylate to the mixed solution under stirring, and stir until the solution is uniform;

[0091] The overall temperature of the uniform solution was lowered to below zero in a microbubble environment, and 0.01 parts of hydrogen peroxide, 0.01 parts of sodium bisulfite, and 0.01 parts of azobis(isobutylene)imidazoline hydrochloride were added dropwise. At the same time, 5 parts of OP-10 were added through nitrogen. The solution was sealed and reacted in a constant temperature water bath at 65°C for 6 hours to form granules. After drying and crushing, a low molecular weight oil displacement polymer suitable for low permeability reservoirs was obtained.

[0092] As shown in Table 2, the low molecular weight oil recovery polymer suitable for low permeability reservoirs prepared in Example 5 has a molecular weight of 7.65 million, a filtration factor of 1.3, an apparent viscosity of 42.8 mPa·s, a shear viscosity retention rate of 93.5%, an injection pressure of 4 MPa, a resistance coefficient of 17, and a residual resistance coefficient of 4.

[0093] Table 1 Components and ratios of each embodiment

[0094]

[0095]

[0096] Table 2 Performance parameters of each embodiment

[0097]

[0098] In summary, the low molecular weight polymer for oil recovery in low permeability reservoirs prepared by the present invention can achieve better salt resistance under the condition of low viscosity average molecular weight (5 million-8 million), and at the same time, the filtration factor is lower, which is more suitable for injection into low permeability reservoirs, and the shear resistance is better, which can reach more than 90%. When the above conditions are met at the same time, the low molecular weight polymer for oil recovery in low permeability reservoirs prepared by the present invention has a dissolution time in water of only 30 minutes, and the dissolution time is even shorter.

[0099] As shown in the table below, with the addition of betaine-type surfactant, the viscosity shows a trend of increasing compared to when no surfactant is added, indicating that the polymer and betaine-type surfactant have a significant viscosity-increasing effect and are suitable for polymer-surfactant binary flooding.

[0100]

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A low molecular weight oil recovery polymer suitable for low permeability reservoirs, characterized in that: Its structural formula is:

2. A low molecular weight oil displacement polymer suitable for low permeability reservoirs according to claim 1, characterized in that: The product is prepared from the following raw materials by weight:

3. A low molecular weight oil displacement polymer suitable for low permeability reservoirs according to claim 1, characterized in that: The organic solvent A is selected from at least one of xylene, tetrachloroethylene, kerosene, diesel, paraffin, ethanol and white oil.

4. A low molecular weight oil displacement polymer suitable for low permeability reservoirs according to claim 1, characterized in that: The organic solvent B is selected from at least one of sorbitan stearate, alkylphenol polyoxyethylene ether, Tween 80, emulsifier A-7, No. 26 white mineral oil, white vaseline, and sorbitol.

5. The low molecular weight oil displacement polymer suitable for low permeability reservoirs according to claim 1, characterized in that: The monomer C is selected from at least one of acrylic acid, methacrylic acid, acrylamide, dimethyldipropylenebenzenesulfonic acid, maleic anhydride and dimethyldipropylenebenzenesulfonate.

6. The low molecular weight oil displacement polymer suitable for low permeability reservoirs according to claim 1, characterized in that: The monomer D is selected from at least one of dimethyldiallylammonium chloride, dimethylaminoethyl methacrylate quaternary ammonium salt, dimethylaminoethyl methacrylate methyl chloride salt, and dimethylaminopropyl acrylamide.

7. The low molecular weight oil displacement polymer suitable for low permeability reservoirs according to claim 1, characterized in that: The monomer E is selected from at least one of methyl acrylate, ethyl acrylate, methyl 2-methacrylate, ethyl 2-methacrylate, hexadecyl acrylate, and fluorocarbon modified acrylate.

8. The low molecular weight oil displacement polymer suitable for low permeability reservoirs according to claim 1, characterized in that: Dispersant F is selected from at least one of silicate, sodium tripolyphosphate, sodium hexametaphosphate, ammonium lauryl sulfate, methyl amyl alcohol, fatty acid polyglycol ester, and OP-10; The initiator G is selected from at least one of hydrogen peroxide, potassium persulfate, sodium persulfate, ammonium persulfate, sodium sulfite, sodium bisulfite, cerium ammonium nitrate, benzoyl peroxide, azobisisobutylamidine hydrochloride, and azobisisobutylimidazoline hydrochloride.

9. A method for preparing a low molecular weight oil displacement polymer suitable for low permeability reservoirs according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) According to the mass percentage, prepare the following raw materials: (2) mixing organic solvent A, organic solvent B and water, maintaining the temperature at 10° C. to 15° C. and stirring to obtain a mixed solution; (3) adding dry ice, monomer C, monomer D, and monomer E to the mixed solution while stirring, and stirring until the solution is uniform to obtain a uniform solution; (4) The overall temperature of the homogeneous solution is reduced to below zero in a microbubble environment, and an initiator G is added dropwise to the homogeneous solution. Meanwhile, a dispersant F is added by nitrogen flow. The solution is sealed and reacted in a constant temperature water bath at 50°C-80°C for 4-8 hours. The solution is then formed into granules, dried, and crushed to obtain a low molecular weight oil recovery polymer suitable for low permeability reservoirs.

10. The preparation method according to claim 9, characterized in that: In step (4), the dripping time of the initiator is controlled within 30 minutes; After sealing, a micro-pressure condition is formed and the mixture is placed in a 50-80°C water bath to react for 4-8 hours.

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