An amphiphilic polymer for oil displacement in low-permeability oil reservoirs and a preparation method thereof

Abstract

The application discloses an amphiphilic polymer for oil displacement in a low-permeability oil reservoir, which comprises a polyacrylamide-sodium acrylate molecular chain, and the polyacrylamide-sodium acrylate molecular chain is introduced with a dodecyl polyoxyethylene (23) ether acrylate structural unit, a dioctyl acrylamide structural unit and a 2-acrylamide-2-methylpropane sulfonic acid sodium structural unit, so as to solve the problem that the recovery ratio improvement value of the existing amphiphilic polymer in a field test has a large improvement space.

Description

Technical Field

[0001] This disclosure relates to the field of tertiary oil recovery technology in oilfield development, and in particular to an amphiphilic polymer for oil displacement in low-permeability reservoirs and its preparation method. Background Technology

[0002] The statements in this section provide only background information in connection with this disclosure and do not constitute prior art.

[0003] In recent years, the penetration rate has been below 200×10 -3 μm 2 These low-permeability reservoirs have become a key target for polymer flooding development in Daqing Oilfield. These reservoirs have geological reserves of approximately 1.86 billion tons, accounting for 44.6% of Daqing Oilfield's total geological reserves, representing significant potential for future growth. Achieving efficient development of these low-permeability reservoirs is crucial for the sustained and stable production of Daqing Oilfield and is a key research focus for polymer flooding in the field.

[0004] Low-permeability reservoirs, due to their low permeability and small pore throat radius, require polymer solutions with reduced molecular weight and injection concentration to penetrate the reservoir and exert their oil displacement effect. However, lowering the molecular weight and injection concentration reduces the viscoelastic displacement mechanism of the polymer, limiting the improvement in oil recovery. Simultaneously, oilfields utilize produced water to prepare and dilute polymer solutions, achieving wastewater recycling. Produced water has a salinity of 4000–7000 mg / L, a pH of 7.5–8.0, and contains iron ions, sulfides, residual polymers, chemical additives, hydrocarbon-degrading bacteria, and NO3. - SO4 2- It contains a variety of microbial communities, including reducing bacteria, saprophytic bacteria, iron bacteria, and fermenting bacteria. Their high mineralization, weak alkalinity, complex composition, and numerous colonies further compress the double electric layer of polymer molecular chains, promote molecular chain hydrolysis and breakage, and significantly reduce their oil displacement performance. This leads to a substantial increase in polymer usage and a significant decline in the technological and economic benefits of polymer flooding.

[0005] Currently, the polymer used for oil displacement in low-permeability reservoirs is mainly partially hydrolyzed polyacrylamide (PHPAM), which is produced by free radical polymerization of acrylamide monomers, followed by hydrolysis of some amide groups to sodium carboxylate. Its molecular weight range is 700 × 10⁻⁶. 4 ~950×10 4 g / mol, with an injection concentration below 2000 mg / L. Completed PHPAM polymer flooding field tests have increased oil recovery by 4.8%–10.2%.

[0006] To further improve the recovery rate of polymer flooding in low-permeability reservoirs, the oilfield adopted two improvement measures. First, it used salt-resistant polymers, which introduce one or more salt-resistant monomers, rigid monomers, and hydrophobic monomers into the PHPAM molecular chain, improving the polymer's performance in produced wastewater through modified copolymerization. Second, it used amphiphilic polymers, which introduce surface-active monomers into the hydrophilic PHPAM molecular chain, resulting in both hydrophilic and lipophilic segments on the same molecular chain. This gives the polymer both viscoelastic and surface-active properties, synergistically improving oil recovery. From the perspective of the oil displacement mechanism, amphiphilic polymers, in addition to the viscoelastic mechanism, also possess surface-active properties, making them more conducive to improving the oil displacement efficiency in low-permeability reservoirs. In terms of field test results, there are currently no completed salt-resistant polymer field tests in low-permeability reservoirs. The ongoing salt-resistant polymer field tests have improved the recovery rate by 9.3%, with a predicted final improvement of 11%–12%; the completed amphiphilic polymer field tests improved the recovery rate by 12.1%. The experimental results of both methods showed a significant improvement in recovery rate compared to PHPAM's 4.8%–10.2%, but there is still room for improvement to reach the goal of efficient development of low-permeability reservoirs.

[0007] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art. Summary of the Invention

[0008] In view of this, this disclosure provides an amphiphilic polymer for oil displacement in low-permeability reservoirs, which solves the problem that there is still a large room for improvement in the recovery value of existing amphiphilic polymers in field tests.

[0009] In addition, this disclosure also provides a method for preparing the amphiphilic polymer for oil displacement in low-permeability reservoirs.

[0010] In the first aspect, the amphiphilic polymer for oil displacement in low-permeability reservoirs includes a polyacrylamide-sodium acrylate molecular chain, wherein a dodecyl polyoxyethylene (23) ether acrylate structural unit and a dioctyl acrylamide structural unit are introduced onto the polyacrylamide-sodium acrylate molecular chain.

[0011] In embodiments of this disclosure, the molecular structural formula of the amphiphilic polymer is as follows:

[0012]

[0013] In the formula, x1, y1, z1, and m1 represent the molar percentage of the corresponding structural unit in the total structural units. Specifically, x1 is 70%–72.5%, y1 is 23%–25%, z1 is 1.5%–2%, and m1 is 100%–x1–y1–z1.

[0014] In embodiments of this disclosure, 2-acrylamide-2-methylpropanesulfonate sodium structural units are introduced onto the polyacrylamide-sodium acrylate molecular chain.

[0015] In embodiments of this disclosure, the molecular structural formula of the amphiphilic polymer is as follows:

[0016]

[0017] In the formula, x2, y2, z2, m2, and n2 represent the molar percentage of the corresponding structural unit in the total structural units. Specifically, x2 is 70%–71.5%, y2 is 23%–25%, z2 is 1.5%–2.0%, n2 is 0.5%–1%, and m2 is 100%–x2–y2–z2–n2.

[0018] Secondly, the method for preparing the amphiphilic polymer for oil displacement in low-permeability reservoirs described in the first aspect includes:

[0019] Polyacrylamide-sodium acrylate and the reaction components composed of various structural units are subjected to oxidation-reduction-initiated free radical polymerization to obtain a polymer colloid;

[0020] The polymer colloid is crushed, dried, pulverized, and sieved to obtain the amphiphilic polymer for oil displacement in low-permeability reservoirs.

[0021] In embodiments of this disclosure, the redox-initiated free radical polymerization is carried out under N2 protection;

[0022] And / or,

[0023] The reaction components also include urea and disodium ethylenediaminetetraacetate;

[0024] And / or,

[0025] The oxidation-reduction initiating polymerization uses potassium persulfate as the oxidizing initiator and sodium bisulfite as the reducing initiator.

[0026] In embodiments of this disclosure, the reaction components are added to water to form a reaction solution;

[0027] The pH value of the reaction solution is 7.0–8.0;

[0028] An antifoaming agent is added to the reaction solution.

[0029] In the embodiments of this disclosure, after the reaction solution undergoes oxidation-reduction initiation polymerization, it is kept at a constant temperature for 12 to 18 hours to mature and obtain the polymer colloid.

[0030] In the embodiments of this disclosure, the polymer colloid is broken into particles and then dried at 60-70°C for 8-12 hours to obtain dried particles; the dried particles are then pulverized and sieved to obtain the amphiphilic polymer for oil displacement in low-permeability reservoirs.

[0031] This disclosure has the following beneficial effects:

[0032] This disclosure discloses an amphiphilic polymer for oil displacement in low-permeability reservoirs. It introduces surface-active structural units, dodecyl polyoxyethylene (23) ether acrylate and dioctyl acrylamide, onto the polyacrylamide-sodium acrylate molecular chain. The introduced dodecyl polyoxyethylene (23) ether acrylate enhances the polymer's surface activity, effectively improving its ability to emulsify crude oil and reduce interfacial tension. The introduced dioctyl acrylamide unit enhances the polymer's thickening and synergistic emulsifying capabilities. Dioctyl acrylamide is a polymerizable monomer with twin-tailed hydrophobic groups; these hydrophobic groups can associate to form a reversible network structure, increasing the structural viscosity of the polymer solution and achieving thickening under wastewater conditions. Simultaneously, the hydrophobic groups can interact with the hydrophobic portion of the surface-active structure, further solubilizing crude oil and improving oil displacement efficiency. Oil displacement experiments using the same dosage show a polymer-driven recovery rate increase of over 15%, making it suitable for the efficient development of low-permeability reservoirs and effectively addressing the issue of limited potential for further increases in the recovery rate of existing amphiphilic polymer field tests. Attached Figure Description

[0033] The above and other objects, features, and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0034] Figure 1 It is the amphiphilic polymer of Embodiment 1 of this disclosure. 1 H NMR spectrum;

[0035] Figure 2 This is the viscosity retention rate as a function of mineralization for different polymers in Experimental Example 2 of this disclosure;

[0036] Figure 3 These are the viscosity-concentration relationship curves of different polymers in Experiment Example 3 of this disclosure;

[0037] Figure 4 This is the viscosity retention rate of different polymers in Experiment Example 4 of this disclosure as a function of aging time.

[0038] Figure 5 These are the injection pressure curves of different polymers in Experimental Example 8 of this publication. Detailed Implementation

[0039] The present disclosure is described below based on embodiments; however, it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, certain specific details are described in detail. However, those skilled in the art will fully understand the present disclosure for the parts not described in detail.

[0040] Furthermore, unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as including rather than exclusive or exhaustive; that is, meaning "including but not limited to."

[0041] This disclosure discloses an amphiphilic polymer for oil displacement in low-permeability reservoirs. To enhance oil recovery under conditions of low permeability and oilfield wastewater, the surface activity of the polymer is improved by introducing the surface-active structural unit dodecyl polyoxyethylene (23) ether acrylate onto the polyacrylamide-sodium acrylate molecular chain. Dodecyl polyoxyethylene (23) ether acrylate is a polymerizable surface-active structural monomer that can effectively improve the polymer solution's properties such as emulsifying crude oil and reducing interfacial tension.

[0042] By introducing dioctylacrylamide structural units into the polyacrylamide-sodium acrylate molecular chain, the thickening and synergistic emulsifying abilities of the polymer are enhanced. Dioctylacrylamide is a polymerizable monomer with twinned hydrophobic groups. The hydrophobic groups can associate to form a reversible network structure, increasing the structural viscosity of the polymer solution and achieving a thickening effect under wastewater conditions. Simultaneously, the hydrophobic groups can interact with the hydrophobic portion of the surface-active structure, further solubilizing crude oil and improving oil displacement efficiency.

[0043] Simultaneously, the salt resistance of the polymer can also be improved by introducing 2-acrylamido-2-methylpropanesulfonate structural units onto the polyacrylamide-sodium acrylate molecular chain. In the molecular structure of 2-acrylamido-2-methylpropanesulfonate, -SO3... - The two π bonds share a negative charge with three strongly negative oxygen atoms, making it insensitive to cation attack and improving the polymer's salt resistance under wastewater conditions; the amide group of sodium 2-acrylamido-2-methylpropanesulfonate is shielded by the adjacent dimethyl group, which can inhibit its hydrolysis to a certain extent and improve the viscosity retention rate in wastewater.

[0044] Based on the above-described inventive concept, this disclosure provides a detailed description of the polymer of the present invention through specific embodiments and experimental examples to further demonstrate its inventive effects.

[0045] The preparation method of the amphiphilic polymer for oil displacement in low-permeability reservoirs according to the following embodiments of this disclosure is carried out using the following steps:

[0046] (1) Weigh the raw materials according to the molar percentage of each structural unit in the polymer molecule. Under stirring conditions, first add acrylamide, sodium acrylate, sodium 2-acrylamide-2-methylpropanesulfonate and small molecule auxiliaries to deionized water and stir until fully dissolved.

[0047] (2) Add dodecyl polyoxyethylene (23) ether acrylate to the solution obtained in step (1) and stir until completely dissolved; then add dioctylacrylamide and continue stirring until completely dissolved.

[0048] (3) Add a 50% NaOH solution to the solution obtained in step (2) and adjust the pH of the solution to 7.0-8.0 to obtain the reaction solution.

[0049] (4) Adjust the temperature of the reaction solution to 0-5℃, add a certain amount of defoamer, and then purge with nitrogen (N2) to remove oxygen for 20 minutes.

[0050] (5) Add a certain amount of redox initiation system to the reaction solution of step (4), and continue to purge with nitrogen (N2) until the reaction solution becomes viscous. Then seal the reaction vessel and allow it to stand and mature under heat preservation conditions for 12-18 hours to obtain the polymer colloid;

[0051] (6) The polymer colloid from step (5) is crushed into colloid particles and dried at 60-70°C for 8-12 hours. The dried colloid particles are then pulverized and sieved to obtain the amphiphilic polymer for low-permeability reservoir oil displacement of the present invention.

[0052] The small molecule auxiliaries in step (1) of this embodiment are urea and disodium ethylenediaminetetraacetate (EDTA-2Na). The amount of urea used is 0.5% of the total mass of the reaction solution, and the amount of disodium ethylenediaminetetraacetate (EDTA-2Na) used is 0.02% of the total mass of the reaction solution.

[0053] In step (4) of this embodiment, the defoamer is polydimethylsiloxane, and the amount used is 0.01% to 0.05% of the total mass of the reaction solution.

[0054] In step (5) of this embodiment, the oxidizing initiator is potassium persulfate (K2S2O8), and the amount used is 0.02% of the total mass of the reaction solution; the reducing initiator is sodium bisulfite (NaHSO3), and the amount used is 0.01% of the total mass of the reaction solution.

[0055] In addition, unless otherwise specified, all materials and reagents used in the following embodiments of this disclosure are commercially available.

[0056] Example 1

[0057] I. The synthesis formula of the amphiphilic polymer for oil displacement in low-permeability reservoirs in Example 1 is as follows (calculated based on a total reaction solution mass of 1000g and a total structural unit mass ratio of 20%):

[0058] Acrylamide (72% molar percentage of structural units): 97.73 g;

[0059] Sodium acrylate (24% molar percentage of structural units): 43.13g;

[0060] Dodecyl polyoxyethylene (23) ether acrylate (2% molar percentage of structural units): 47.87 g;

[0061] Dioctylacrylamide (2% molar percentage of structural units): 11.28 g;

[0062] Urea (0.5% of the total mass of the reaction solution): 5.0g;

[0063] Disodium ethylenediaminetetraacetate (0.02% of the total mass of the reaction solution): 0.2 g;

[0064] Sodium hydroxide (50% aqueous solution): 37.27g.

[0065] Deionized water: 757.52g;

[0066] Polydimethylsiloxane (0.02% of the total mass of the reaction solution): 0.2g;

[0067] Potassium persulfate (5% aqueous solution, 0.02% of the total mass of the reaction solution): 4 mL;

[0068] Sodium bisulfite (5% aqueous solution, 0.01% of the total mass of the reaction solution): 2 mL;

[0069] II. The amphiphilic polymer for oil displacement in low-permeability reservoirs in Example 1 was prepared using the following method:

[0070] (1) Weigh the raw materials according to the mass ratio and set solution concentration, and prepare a solution of NaOH, potassium persulfate initiator, and sodium bisulfite. Under the condition of electric stirring at 400 rpm, add acrylamide, sodium acrylate, urea, and disodium ethylenediaminetetraacetate to deionized water in sequence and stir until fully dissolved;

[0071] (2) Add dodecyl polyoxyethylene (23) ether acrylate to the solution obtained in step (1) and stir with an electric stirrer at 400 rpm until completely dissolved; then add dioctylacrylamide and continue stirring until completely dissolved;

[0072] (3) Add a 50% NaOH solution to the solution obtained in step (2) and adjust the pH of the solution to 7.5 to obtain the reaction solution;

[0073] (4) Place the container in a 0℃ water bath, add defoamer polydimethylsiloxane, and then purge with nitrogen (N2) for 20 minutes to remove oxygen.

[0074] (5) Add sodium bisulfite solution to the reaction solution from step (4), followed by potassium persulfate solution, and continue to purge with nitrogen (N2) until the reaction solution becomes viscous. Then seal the reaction vessel and allow it to stand and mature under heat for 18 hours to obtain the polymer colloid.

[0075] (6) The polymer colloid from step (5) is crushed into colloid particles, dried at 65°C for 8 hours, and then the dried colloid particles are crushed and sieved to a size of 0.1 mm to 0.15 mm to obtain the amphiphilic polymer for oil displacement in low-permeability reservoirs as described in Example 1.

[0076] III. Structural characterization of the amphiphilic polymer for oil displacement in low-permeability reservoirs described in Example 1:

[0077] 1. The structure of the amphiphilic polymer used for oil displacement in low-permeability reservoirs in Example 1 was characterized using an 800MHz nuclear magnetic resonance spectrometer manufactured by Bruker AG, Switzerland. An appropriate amount of polymer was fully dissolved in D2O and transferred to an NMR tube. Its structure was then measured using an 800MHz high-resolution NMR spectrometer. 1 H NMR. Test results are attached. Figure 1 As shown, Figure 1 shown 1 The HNMR spectrum analysis is as follows:

[0078] (1) The spectrum is mainly concentrated between 0.4 and 4.0 ppm, and no absorption peaks were found above 4.0 ppm, indicating that the polymer molecule does not contain a benzene ring structure;

[0079] (2) There are two obvious peaks at 6.5 to 6.9 ppm. By comparison, it was found that the peaks originated from the proton peaks of -NH2 and -NHD in the acrylamide structure (generated by the exchange of protons between -NH2 and solvent D2O).

[0080] (3) Among all chemical shifts, 1.2 ppm and 1.9 ppm have the largest integral areas. The 1.2 ppm position is a doublet of -CH2 in the acrylamide and sodium acrylate structures of the polymer, and the 1.9 ppm position is a triplet of -CH in the acrylamide and sodium acrylate structures of the polymer.

[0081] (4) The single peak at 3.65 ppm is the proton peak at the end of -CH2-CH3, and the broad peak at 3.45 to 3.52 ppm is the proton peak of -CH2CH2O.

[0082] (5) The multiple peaks at 2.56 ppm are the proton peaks of CH2 near -N in the structure of dioctylacrylamide, and the broad peaks at 2.35 to 2.45 ppm are the proton peaks of -CH2CH2-.

[0083] 1 1H NMR spectral analysis results show that the amphiphilic polymer in Example 1 has four structural units: acrylamide, sodium acrylate, dodecyl polyoxyethylene (23) ether acrylate, and dioctylacrylamide. This indicates that the amphiphilic polymer for oil displacement in low-permeability reservoirs described in this disclosure has been successfully prepared, and also confirms the authenticity of the copolymerization reaction of the four monomers.

[0084] Example 2

[0085] The synthesis formulation of the amphiphilic polymer for oil displacement in low-permeability reservoirs in Example 2 is as follows (calculated based on a total reaction solution mass of 1000g and a total structural unit mass percentage of 25%):

[0086] Acrylamide (71% molar percentage of structural units): 118.67 g;

[0087] Sodium acrylate (24% molar percentage of structural units): 53.11 g;

[0088] Sodium 2-acrylamide-2-methylpropanesulfonate (1% molar percentage of structural units): 5.39 g;

[0089] Dodecyl polyoxyethylene (23) ether acrylate (2% molar percentage of structural unit): 58.95g;

[0090] Dioctylacrylamide (2% molar percentage of structural units): 13.89 g;

[0091] Urea (0.5% of the total mass of the reaction solution): 5.0g;

[0092] Disodium ethylenediaminetetraacetate (0.02% of the total mass of the reaction solution): 0.2 g;

[0093] Sodium hydroxide (50% aqueous solution): 45.45g.

[0094] Deionized water: 699.34g;

[0095] Polydimethylsiloxane (0.02% of the total mass of the reaction solution): 0.2g;

[0096] Potassium persulfate (5% aqueous solution, 0.02% of the total mass of the reaction solution): 4 mL;

[0097] Sodium bisulfite (5% aqueous solution, 0.01% of the total mass of the reaction solution): 2 mL;

[0098] Compared to Example 1, Example 2 changed the raw material ratio and added the salt-resistant monomer sodium 2-acrylamide-2-methylpropanesulfonate. The preparation method used in Example 2 is the same as that in Example 1.

[0099] Example 3

[0100] The synthesis formulation of the amphiphilic polymer for oil displacement in low-permeability reservoirs in Example 3 is as follows (calculated based on a total reaction solution mass of 1000g and a total structural unit mass percentage of 23%):

[0101] Acrylamide (70% molar percentage of structural units): 105.41 g;

[0102] Sodium acrylate (24% molar percentage of structural units): 47.85g;

[0103] Sodium 2-acrylamide-2-methylpropanesulfonate (1% molar percentage of structural units): 4.86 g;

[0104] Dodecyl polyoxyethylene (23) ether acrylate (2% molar percentage of structural unit): 53.11 g;

[0105] Dioctylacrylamide (3% molar percentage of structural units): 18.77g;

[0106] Urea (0.5% of the total mass of the reaction solution): 5.0g;

[0107] Disodium ethylenediaminetetraacetate (0.02% of the total mass of the reaction solution): 0.2 g;

[0108] Sodium hydroxide (50% aqueous solution): 40.55g.

[0109] Deionized water: 724.25g;

[0110] Polydimethylsiloxane (0.02% of the total mass of the reaction solution): 0.2g;

[0111] Potassium persulfate (5% aqueous solution, 0.02% of the total mass of the reaction solution): 4 mL;

[0112] Sodium bisulfite (5% aqueous solution, 0.01% of the total mass of the reaction solution): 2 mL;

[0113] Compared to Examples 1 and 2, Example 3 increases the molar percentage of the hydrophobic monomer dioctylacrylamide. The preparation method of Example 3 is the same as that of Example 1.

[0114] Experimental Example 1

[0115] This experimental example focuses on the evaluation of the basic physicochemical properties of Examples 1-3 and the comparative polymers. The comparative polymers described in this experimental example have all undergone field trials in the low-permeability reservoirs of the Daqing Oilfield, and include partially hydrolyzed polyacrylamide (PHPAM), salt-resistant polymer KYPAM, and type BIII amphiphilic polymer.

[0116] This experiment, Example 1, is based on the People's Republic of China petroleum and natural gas industry standard "SY / T5862-2020 Technical Requirements for Polymers Used for Oil Displacement". It evaluates Examples 1 to 3 and compares the performance indicators of polymers PHPAM, KYPAM, and BIII, including molecular weight, solid content, degree of hydrolysis, water-insoluble matter, filtration factor, apparent viscosity, and dissolution rate. The results are shown in Table 1.

[0117] Table 1. Basic physicochemical properties of Examples 1-3 and comparative polymers.

[0118] Physicochemical indicators Standard requirements Example 1 Example 2 Example 3 PHPAM KYPAM BIII <![CDATA[Molecular weight (×10 4 g / mol)]]> 700～950 832 846 850 799 845 778 Solid content (wt%) ≥88.0 90.6 90.2 90.5 89.9 9.03 91.5 Degree of hydrolysis (mol%) 23％～27％ 23.5 23.6 24.5 24.1 23.8 23.4 Water-insoluble matter (wt%) ≤0.20 0.16 0.15 0.12 0.05 0.10 0.18 Filtering factor ≤1.5 1.08 1.07 1.01 0.55 1.06 1.33 Apparent viscosity (mPa·s) ≥19 22.7 24.2 28.7 20.1 24.8 19.8 Dissolution rate (h) ≤2.0 1.5 1.5 1.4 1.2 1.5 1.5

[0119] As shown in Table 1, the basic physicochemical properties of the polymers in Examples 1-3 and the comparative polymers all meet industry standards. The molecular weights of the polymers are all between 700 and 950 × 10⁻⁶. 4 Between g / mol, suitable for low-permeability reservoirs.

[0120] Experimental Example 2

[0121] This second experimental example aims to compare and evaluate the salt resistance properties of Example 1, Example 2, and the comparative polymers PHPAM, KYPAM, and BIII under different mineralization conditions. The performance evaluation process of this second experimental example is as follows:

[0122] (1) Prepare a polymer mother liquor with a concentration of 2000 mg / L using simulated clean water (0.095 wt% NaCl solution);

[0123] (2) The above mother liquor was then diluted with simulated sewage (2.0 wt% NaCl solution) to form a polymer solution with a concentration of 1000 mg / L and mineralization of 0.095 wt%, 0.241 wt%, 0.4 wt%, 0.7 wt% and 1.0 wt%, respectively.

[0124] (3) The viscosity of polymer solutions with different mineralization degrees was determined using a Brookfield DV-II+ viscometer. The measurement process was performed using a 0°C setting. # Rotor, rotational speed 6 rpm, shear rate 7.338 s. -1 The measured temperature was 45℃.

[0125] (4) Using the viscosity of the polymer solution with a mineralization of 0.095 wt% as a benchmark, divide the viscosity of the polymer solution with each mineralization by this benchmark, and plot the viscosity retention rate as a function of mineralization, as shown in the figure. Figure 2 As shown.

[0126] Figure 2 The evaluation results show that, under the same salinity conditions, the BIII amphiphilic polymer exhibits the worst salt resistance, with a viscosity retention rate lower than PHPAM. The viscosity retention rates of the other polymers are all higher than PHPAM, with Example 2 showing the highest viscosity retention rate. Example 2, which incorporates an additional salt-resistant monomer, sodium 2-acrylamide-2-methylpropanesulfonate, compared to Example 1, shows a higher viscosity retention rate under the same salinity conditions, verifying that sodium 2-acrylamide-2-methylpropanesulfonate can improve the salt resistance of the polymer. Examples 1 and 2 demonstrate good salt resistance, which is beneficial for improving the polymer's application performance in oilfield wastewater.

[0127] Experiment Example 3

[0128] This third experimental example aims to compare and evaluate the thickening properties of Example 1, Example 3, and the comparative polymers PHPAM, KYPAM, and BIII under oilfield wastewater conditions.

[0129] In Experiment Example 3, the water samples used for preparing and diluting the polymer solution were taken from the polymer preparation station at the oilfield. The performance evaluation process for Experiment Example 3 is as follows:

[0130] (1) Prepare a polymer mother liquor with a concentration of 5000 mg / L using clean water on site;

[0131] (2) The above mother liquor was then diluted with on-site sewage to form a polymer solution of 50g with a concentration of 600-1500mg / L;

[0132] (3) The viscosity of polymer solutions of different concentrations was measured using a Brookfield DV-II+ viscometer. The measurement process was performed using a 0°C setting. # Rotor, rotational speed 6 rpm, shear rate 7.338 s. -1 The measured temperature was 45℃.

[0133] (4) Based on the measurement results, plot the viscosity-concentration relationship curves for different polymers, such as... Figure 3 As shown.

[0134] Depend on Figure 3 As can be seen, the viscosity of all polymers increases with increasing concentration. Under the same concentration conditions, the BIII amphiphilic polymer has the lowest viscosity, while Examples 1 and 3 have the highest viscosity. The viscosity of Example 3 is higher than that of Example 1 because Example 3 has a higher molar proportion of the hydrophobic monomer dioctylacrylamide than Example 1, which also verifies that the addition of hydrophobic monomers can improve the thickening properties of amphiphilic polymers. The better thickening properties of amphiphilic polymers are beneficial to exerting the viscoelastic oil displacement mechanism of polymers and improving oil displacement efficiency.

[0135] Experiment Example 4

[0136] This fourth experimental example aims to compare and evaluate the heat resistance stability of the polymer in Example 3 under oilfield wastewater conditions with the control polymers PHPAM, KYPAM, and BIII.

[0137] In Experiment Example 4, the water samples used for preparing and diluting the polymer solution were taken from the polymer preparation station at the oilfield. The performance evaluation process for Experiment Example 4 is as follows:

[0138] (1) Prepare a polymer mother liquor with a concentration of 5000 mg / L using clean water on site;

[0139] (2) The above mother liquor was then diluted with on-site sewage to form a polymer solution with a concentration of 1000 mg / L and a weight of 50 g.

[0140] (3) The diluted solution is put into ampoules and deoxygenated using the iHDAS-Ⅱ intelligent high-efficiency deoxygenation system (Beijing Donghang Scientific Instruments Co., Ltd.). The ampoules are then melted and sealed and placed in a 45℃ constant temperature chamber for constant temperature aging.

[0141] (4) Measure the viscosity of the solution at different aging times, divide it by the initial viscosity, calculate the viscosity retention rate, and plot the viscosity retention rate versus aging time curve, such as... Figure 4 As shown. Viscosity was measured using a Brookfield DV-II+ viscometer, with the measurement process selected as 0. # Rotor, rotational speed 6 rpm, shear rate 7.338 s. -1 The measured temperature was 45℃.

[0142] Depend on Figure 4 It is evident that the viscosity retention rates of different polymer solutions all decreased with aging time. At the same aging time, PHPAM exhibited the lowest viscosity retention rate, while Example 3 showed the highest. This is because Example 3 introduced a sodium 2-acrylamide-2-methylpropanesulfonate structural unit, whose amide group was shielded by the adjacent dimethyl group, thus inhibiting hydrolysis to some extent. Furthermore, the hydrophobic interactions between the dioctylacrylamide and dodecyl polyoxyethylene (23) ether acrylate hydrophobic components formed a network structure, further inhibiting amide group hydrolysis. The amphiphilic polymer of Example 3 exhibited good thermal stability, which is beneficial for maintaining a high working viscosity under anaerobic reservoir conditions.

[0143] Experimental Example 5

[0144] This fifth experimental example is to evaluate the emulsified crude oil type of the polymers in Examples 1-3, and to compare the polymers PHPAM, KYPAM, and BIII.

[0145] In Experiment Example 5, the crude oil used for emulsification was dehydrated and degassed crude oil from the Daqing Oilfield Joint Station. The performance evaluation process for Experiment Example 5 is as follows:

[0146] (1) A polymer mother liquor with a concentration of 5000 mg / L was prepared using simulated clean water (0.095 wt% NaCl solution), and then the above mother liquor was diluted with simulated sewage (0.45 wt% NaCl solution) to a polymer solution with a concentration of 1000 mg / L.

[0147] (2) Add 10 mL of polymer solution and 10 mL of dehydrated crude oil to a 25 mL stoppered colorimetric tube, and place the stoppered colorimetric tube in a 45 °C constant temperature oven for 1 hour to preheat.

[0148] (3) Vigorously shake the stoppered colorimetric tube 100 times to fully mix the oil and water. Immediately use a dropper to transfer 1 drop of the emulsion into a beaker containing 45°C deionized water. Gently shake the beaker and observe whether the oil drop disperses. If the emulsion disperses quickly, it is an O / W type (oil-in-water emulsion); if the emulsion does not disperse, it is a W / O type (water-in-oil emulsion).

[0149] The results of emulsification type are shown in Table 2. As can be seen from Table 2, PHPAM and KYPAM cannot emulsify crude oil. Examples 1-3 and the BIII amphiphilic polymers form O / W type emulsions with crude oil.

[0150] Table 2. Types of Emulsified Crude Oils with Different Polymers

[0151] polymer Example 1 Example 2 Example 3 PHPAM KYPAM BIII Emulsion type O / W O / W O / W Non-emulsification Non-emulsification O / W

[0152] Experimental Example 6

[0153] This sixth experimental example aims to evaluate the emulsification water separation rate of the emulsions formed by emulsifying crude oil using the polymers of Examples 1-3 and the comparative polymer BIII.

[0154] In Experiment Example 6, the crude oil used for emulsification was dehydrated and degassed crude oil from the Daqing Oilfield Joint Station. The performance evaluation process for Experiment Example 6 is as follows:

[0155] (1) A polymer mother liquor with a concentration of 5000 mg / L was prepared using simulated clean water (0.095 wt% NaCl solution), and then the above mother liquor was diluted with simulated sewage (0.45 wt% NaCl solution) to a polymer solution with a concentration of 1000 mg / L.

[0156] (2) Add 10 mL of polymer solution and 10 mL of dehydrated crude oil to a 25 mL stoppered colorimetric tube, and read the volume of the lower aqueous phase in the stoppered colorimetric tube, which is marked as V1.

[0157] (3) After preheating the stoppered colorimetric tube in a 45°C constant temperature box for 1 hour, shake it vigorously 100 times to mix the oil and water thoroughly, and then put it in a 45°C constant temperature box to stand.

[0158] (4) Record the volume of the lower aqueous phase in the stoppered colorimetric tube at different settling times, and label it as V2. Also record the emulsification separation rate P. w =V2 / V1×100%.

[0159] Table 3 shows the emulsion water separation rates of different polymers and crude oil emulsions.

[0160] Table 3. Emulsion water separation rate of emulsions formed by different polymers and crude oil

[0161]

[0162] The data in Table 3 show that the emulsion water separation rate of Examples 1-3 and the BIII amphiphilic polymer gradually increased with the standing time, and all exceeded 90% after 24 hours. Since the polymer is suitable for low-permeability reservoirs, the higher emulsion water separation rate is conducive to the timely demulsification of the emulsion, will not cause blockage of the pore throat, and is conducive to the movement of fluid.

[0163] Experimental Example 7

[0164] This Experimental Example 7 aims to evaluate the performance of the polymers in Examples 1-3, and the comparative polymers PHPAM, KYPAM, and BIII in reducing the interfacial tension between oil and water.

[0165] In this Experiment Example 7, the crude oil used for emulsification was dehydrated and degassed crude oil from the Daqing Oilfield Joint Station. This Experiment Example 7 utilized a TVT2 interfacial tension instrument (LAUDA, Germany) to measure the interfacial tension. The specific procedure is as follows:

[0166] (1) Prepare a polymer mother liquor with a concentration of 5000 mg / L using simulated clean water (0.095 wt% NaCl solution), and then dilute the above mother liquor with simulated sewage (0.45 wt% NaCl solution) to a polymer solution with a concentration of 1000 mg / L.

[0167] (2) Preheat the polymer solution, dehydrated crude oil, and tensiometer water bath to 45°C;

[0168] (3) Fill the sample cell with the polymer solution to be tested, use a U-shaped syringe to draw up the dehydrated crude oil, and then reinstall them at the measurement positions.

[0169] (4) Start the tension meter to measure 10 drops for each sample and take the median as the result.

[0170] Table 4 shows the interfacial tensions between different polymer solutions and crude oil. The data in Table 4 indicate that the interfacial tension between PHPAM and crude oil is 60.1 mN·m. -1 The interfacial tension values ​​of the polymers and crude oil in Examples 1-3 were as low as 3.1 mN·m. -1 Experimental results show that the polymers in Examples 1-3 can effectively reduce the interfacial tension between oil and water.

[0171] Table 4 Interfacial tension between different polymer solutions and crude oil

[0172] polymer <![CDATA[Interfacial tension (mN·m -1 )]]> Example 1 5.2 Example 2 5.1 Example 3 3.1 PHPAM 60.1 KYPAM 55.3 BIII 8.3

[0173] Experimental Example 8

[0174] This eighth experiment aims to evaluate the injection performance of the polymers of Examples 1-3, and the comparative polymers PHPAM, KYPAM, and BIII solutions in low-permeability reservoirs.

[0175] In Example 8 of this experiment, the water samples used for preparing and diluting the polymer solution were taken from the polymer preparation station at the oilfield. The core samples used in the experiment were obtained from a natural sandstone reservoir. Under conditions of constant wettability, the cores were soaked in solvent gasoline and dried. The cores were approximately 2.5 cm in diameter and 10 cm in length, with an effective permeability of less than 200 × 10⁻⁶. -3 μm 2 .

[0176] The injection performance of polymers in low-permeability cores was evaluated using the QY-C12 multifunctional polymer flooding unit (Jiangsu Huaan Technology Co., Ltd.). The specific process is as follows:

[0177] (1) Prepare a polymer mother liquor with a concentration of 5000 mg / L using clean water on site, and then dilute it with wastewater on site to a polymer solution with a concentration of 1000 mg / L.

[0178] (2) After measuring and recording the specifications of the core, the core is evacuated for 2 hours;

[0179] (3) Fill the evacuated core with saturated wastewater at a specific rate, record the wastewater volume V when the pressure gauge value returns to zero, and calculate the core pore volume PV and porosity Φ.

[0180] (4) Inject wastewater at a rate of 5.0 cm3 / min, record the pressure difference ΔP when the pressure is stable, and calculate the effective permeability K of the core according to Darcy's law;

[0181] (5) With 0.6cm 3 The wastewater was injected into the site at a rate of / min for water driving, and the pressure difference ΔP1 when the pressure was stable was recorded.

[0182] (6) With 0.6cm 3The polymer solution was injected at a rate of / min, and the pressure difference ΔP2 was recorded when the pressure was stable.

[0183] (7) With 0.6cm 3 The wastewater was injected again at a rate of / min for subsequent water drive, and the pressure difference ΔP3 was recorded when the pressure was stable.

[0184] (8) Calculate the drag coefficient F based on the pressure difference. r With residual drag coefficient F rr .

[0185] The drag coefficient is F r =ΔP2 / ΔP1, residual drag coefficient F rr =ΔP3 / ΔP1.

[0186] The experimental results and pressure curves are shown in Table 5 and Appendix. Figure 5 .

[0187] Table 5. Injection performance of different polymers in low-permeability reservoirs

[0188] polymer Penetration rate (mD) <![CDATA[Drag coefficient F r > <![CDATA[Residual resistance coefficient F rr > Example 1 108.48 25.23 8.23 Example 2 112.56 26.12 8.26 Example 3 121.02 26.78 8.33 PHPAM 130.25 15.35 5.08 KYPAM 124.26 21.56 7.15 BIII 118.59 19.26 6.01

[0189] From the appendix Figure 5 As shown in Table 5, the pressure curves of all flow experiments plateaued during the polymer flooding stage, followed by a rapid decrease in pressure during the subsequent water flooding stage, and then fluctuated slightly around a certain value. The drag coefficient and residual drag coefficient values ​​of the flow experiments were both small, and the residual drag coefficient was less than 1 / 3 of the drag coefficient, indicating that the polymers of Examples 1-3 of this disclosure, as well as the comparative polymers PHPAM, KYPAM, and BIII, can be effectively injected into low-permeability reservoirs.

[0190] Experiment Example 9

[0191] This Experimental Example 9 aims to evaluate the oil displacement efficiency of the polymers in Examples 1-3, and to compare the efficiency of polymers PHPAM, KYPAM, and BIII.

[0192] In Example 9 of this experiment, the water samples used for preparing and diluting the polymer solution were taken from the polymer preparation station at the oilfield. The simulated crude oil used in the experiment was a mixture of dehydrated and degassed crude oil from Daqing Oilfield and aviation kerosene, with a viscosity of 10.2 mPa·s at 45°C. The core samples used in the experiment were drilled from natural sandstone reservoirs, and after being soaked in solvent gasoline and dried under conditions of constant wettability, the cores were approximately 2.5 cm in diameter and 10 cm in length, with an effective permeability of less than 200 × 10⁻⁶. -3 μm 2 .

[0193] The oil displacement efficiency of polymer in low-permeability cores was evaluated using the QY-C12 multifunctional polymer flooding unit (Jiangsu Huaan Technology Co., Ltd.). The specific process is as follows:

[0194] (1) Prepare a polymer mother liquor with a concentration of 5000 mg / L using fresh water on site, and then dilute the mother liquor with wastewater on site to a polymer solution with a concentration of 1000 mg / L.

[0195] (2) After measuring and recording parameters such as the length L and diameter D of the core, the core is placed in the holder and ΔP is applied. r Vacuuming was performed for 2 hours to achieve a ring pressure of 3 MPa;

[0196] (3) Saturate the core with simulated sewage at a specific rate, record the volume of simulated sewage V1 when the pressure gauge value returns to zero, and calculate the pore volume PV and porosity Φ of the core.

[0197] (4) Inject simulated sewage at different rates, record the pressure difference ΔP when the pressure is stable, calculate the effective permeability K of the core according to Darcy's law, and take the average rate after multiple measurements.

[0198] (5) Saturate the simulated crude oil at different rates until the water content of the produced liquid is 0, record the volume of simulated water removed (V2), and calculate the original saturation level (S). o The core samples were then matured at 45°C for 24 hours after being saturated with simulated oil.

[0199] (6) With 0.2cm 3 The wastewater was injected at a rate of / min for water drive until the water content of the produced liquid reached 98%.

[0200] (7) With 0.2cm 3 Polymer drive was performed by injecting a polymer solution with a concentration of 1000 mg / L at a rate of 0.7 PV / min.

[0201] (8) With 0.2cm 3 The wastewater was injected again at a rate of / min for subsequent water flooding until the water content of the produced liquid reached 98% again, at which point the oil displacement experiment ended.

[0202] Calculate the waterflood recovery rate R based on the oil production at each stage. w Polymer-driven oil recovery rate R p and total recovery rate R t The results of the oil displacement are shown in Table 6.

[0203] Table 6 Oil displacement efficiency of different polymers

[0204] polymer K / (mD) <![CDATA[S o / (%)]]> <![CDATA[R w (%)]]> <![CDATA[R p / (%)]]> <![CDATA[R t / (%)]]> Example 1 120.5 63.6 46.3 15.1 61.4 Example 2 133.7 63.8 47.1 15.7 62.8 Example 3 114.3 62.2 46.8 16.5 63.3 PHPAM 130.4 64.1 46.0 9.8 55.8 KYPAM 132.5 63.8 45.8 11.7 57.5 BIII 118.6 62.2 47.8 12.0 59.8

[0205] Table 6 shows the results of the oil displacement experiments. PHPAM polymer flooding increased the oil recovery rate of low-permeability reservoirs by 9.8%, and the use of salt-resistant polymers and amphiphilic polymers can further improve the oil displacement efficiency. Specifically, the salt-resistant polymer KYPAM increased the recovery rate by 11.7%, and the amphiphilic polymer BIII increased it by 12.0%, but there is still room for improvement to significantly increase the recovery rate. Examples 1-3 of this disclosure can increase the recovery rate by more than 15%, which is 3-5 percentage points higher than the comparative polymers PHPAM, KYPAM, and BIII, indicating that the amphiphilic polymers prepared in Examples 1-3 of this disclosure meet the requirements for efficient development of low-permeability reservoirs.

[0206] The embodiments described above are merely illustrative of implementation methods of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent disclosure. It should be noted that those skilled in the art can make various modifications, equivalent substitutions, and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent disclosure should be determined by the appended claims.

Claims

1. An amphiphilic polymer for oil displacement in low-permeability reservoirs, comprising a polyacrylamide-sodium acrylate molecular chain, characterized in that: Dodecyl polyoxyethylene (23) ether acrylate structural units and dioctyl acrylamide structural units are introduced into the polyacrylamide-sodium acrylate molecular chain. The molecular structural formula of the amphiphilic polymer is: In the formula, x1, y1, z1, and m1 are the molar percentages of the corresponding structural units in the total structural units, where x1 is 70% to 72.5%, y1 is 23% to 25%, z1 is 1.5% to 2%, and m1 is 100% - x1 - y1 - z1.

2. The amphiphilic polymer according to claim 1, characterized in that: Sodium 2-acrylamide-2-methylpropanesulfonate structural units are introduced into the polyacrylamide-sodium acrylate molecular chain.

3. The amphiphilic polymer according to claim 2, characterized in that, The molecular structural formula of the amphiphilic polymer is: In the formula, x2, y2, z2, m2, and n2 are the molar percentages of the corresponding structural units in the total structural units, where x2 is 70%–71.5%, y2 is 23%–25%, z2 is 1.5%–2.0%, n2 is 0.5%–1%, and m2 is 100%–x2–y2–z2–n2.

4. The method for preparing the amphiphilic polymer for oil displacement in low-permeability reservoirs according to any one of claims 1-3, characterized in that, include: Polyacrylamide-sodium acrylate and the reaction components composed of various structural units are subjected to oxidation-reduction-initiated free radical polymerization to obtain a polymer colloid; The polymer colloid is crushed, dried, pulverized, and sieved to obtain the amphiphilic polymer for oil displacement in low-permeability reservoirs.

5. The method for preparing the amphiphilic polymer according to claim 4, characterized in that: The free radical polymerization was carried out under N2 protection.

6. The method for preparing the amphiphilic polymer according to claim 4, characterized in that: The reaction components also include urea and disodium ethylenediaminetetraacetate.

7. The method for preparing the amphiphilic polymer according to claim 4, characterized in that: The oxidation-reduction initiating polymerization uses potassium persulfate as the oxidizing initiator and sodium bisulfite as the reducing initiator.

8. The method for preparing the amphiphilic polymer according to claim 5 or 6, characterized in that: The oxidation-reduction initiating polymerization uses potassium persulfate as the oxidizing initiator and sodium bisulfite as the reducing initiator.

9. The method for preparing the amphiphilic polymer according to claim 6, characterized in that: The reaction components are added to water to form a reaction solution; The pH value of the reaction solution is 7.0–8.0; An antifoaming agent is added to the reaction solution.

10. The method for preparing the amphiphilic polymer according to claim 9, characterized in that: After the reaction solution undergoes oxidation-reduction polymerization, it is kept at a constant temperature and allowed to stand for 12-18 hours to mature, thereby obtaining the polymer colloid.

11. The method for preparing the amphiphilic polymer according to claim 10, characterized in that: After the polymer colloid is broken into granules, it is dried at 60-70°C for 8-12 hours to obtain dried granules; the dried granules are then pulverized and sieved to obtain the amphiphilic polymer for oil displacement in low-permeability reservoirs.

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