An environmentally responsive polymer for high temperature low calcium reservoirs and a method of making the same

Abstract

The present disclosure relates to an environment-responsive polymer for high-temperature low-calcium oil reservoirs and a preparation method thereof, the environment-responsive polymer for high-temperature low-calcium oil reservoirs, by mole percentage, its components include: temperature-resistant monomer: 1.5mol%-3.5mol%, acrylamide: 80mol%-91mol%, divalent metal ion synergistic monomer: 7mol%-18mol%, and the balance is water; the present disclosure makes full use of a small amount of divalent metal ions in the oil reservoir environment, realizes thickening effect through the synergistic effect of divalent metal ions and the polymer, and significantly improves the thermal stability, viscosity increasing effect, environmental responsiveness and temperature resistance of the polymer, converts the adverse conditions into favorable conditions, improves the application performance of the polymer in the high-temperature low-calcium oil reservoir, and provides a new and efficient polymer for oil displacement for the development of high-temperature low-calcium oil reservoirs.

Description

Technical Field

[0001] This disclosure relates to the field of polymer flooding for enhanced oil recovery, specifically to an environmentally responsive polymer for high-temperature, low-calcium reservoirs. Background Technology

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

[0003] Traditional polymer flooding primarily utilizes two types of polymers: synthetic polymers and natural polymers. Partially hydrolyzed polyacrylamide (HPAM) is the most widely used synthetic polymer. HPAM readily undergoes hydrolysis at high temperatures, increasing the degree of hydrolysis and carboxyl content. In highly salinized formation water, high concentrations of divalent metal ions (Ca) are present. 2+ and Mg 2+ HPAM molecules bind to carboxyl groups through electrostatic interactions, weakening the charge on the polymer chains and causing them to coil or even flocculate. Therefore, HPAM is unsuitable for high-temperature, high-salinity reservoirs. Another widely used natural polymer is xanthan gum. Although xanthan gum is more stable than HPAM at higher salinity and temperatures, it degrades under high-temperature, high-salinity conditions. Therefore, xanthan gum is also unsuitable for high-temperature, high-salinity reservoirs.

[0004] To suit high-temperature, high-salinity oil reservoirs, products such as temperature-resistant and salt-resistant monomer copolymers, hydrophobic associative polymers, temperature-increasing viscosity polymers, and nanoparticle-reinforced polymers have been developed. The development of high-temperature, high-salinity oil reservoirs has led to continuous advancements in the research of temperature-resistant and salt-resistant polymers. Furthermore, the development of special types of oil reservoirs such as offshore oilfields and heavy oil reservoirs has also promoted the synthesis and research of special types of polymers such as fast-dissolving polymers and amphiphilic polymers.

[0005] The ongoing research and development of polymers for oil displacement is attributed to the gradual development of different types of reservoirs. However, current research focuses primarily on conventional reservoirs with low to medium temperatures and low salinity, as well as harsh reservoir environments such as high temperature and high salinity. Insufficient attention has been paid to the development of polymers for oil displacement in reservoirs with high temperatures (80-95℃), medium salinity (slightly above 3000 mg / L), and low calcium and magnesium (<100 mg / L), such as the Rokan Block in Indonesia. Consequently, no polymers specifically designed for this type of reservoir have been developed. While several temperature- and salt-resistant polymers exist, their relatively low molecular weight and the disruption of intermolecular forces at high temperatures have prevented them from exhibiting excellent stability and viscosity-enhancing properties under high-temperature, low-calcium reservoir conditions.

[0006] 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

[0007] In view of this, this disclosure provides an environmentally responsive polymer for high-temperature, low-calcium reservoirs and its preparation method, which solves the problem that existing temperature-resistant and salt-resistant polymers have poor thermal stability and lack viscosity-enhancing properties under high-temperature, low-calcium reservoir conditions.

[0008] To achieve the above-mentioned objective, in a first aspect, the environmentally responsive polymer for high-temperature, low-calcium oil reservoirs, by molar percentage, comprises:

[0009] Temperature-resistant monomers: 1.5 mol%-3.5 mol%, acrylamide: 80 mol%-91 mol%, monomers that synergize with divalent metal ions: 7 mol%-18 mol%, balance is water.

[0010] In this disclosure and possible embodiments, the reservoir temperature of the high-temperature, low-calcium reservoir is 80℃-95℃, the mineralization is not higher than 6000mg / L, and the calcium and magnesium ion concentration is not higher than 100mg / L.

[0011] In this disclosure and possible embodiments, the heat-resistant monomer is selected from one or any mixture of several of N-vinylpyrrolidone, N,N-dimethylacrylamide, sodium styrene sulfonate, sodium 2-acrylamido-2-methylpropanesulfonate, N-phenylethyl-N-dodecylmethylacrylamide, and N-dodecylacrylamide.

[0012] In this disclosure and possible embodiments, the monomer that synergizes with the divalent metal ion is selected from one or more of acrylic acid, sodium acrylate, methacrylic acid, sodium methacrylate, and maleic acid.

[0013] Second, the method for preparing the environmentally responsive polymer according to any one of the first aspects includes:

[0014] Acrylamide, a heat-resistant monomer, and a monomer that synergizes with divalent metal ions are copolymerized to obtain the environmentally responsive polymer.

[0015] In this disclosure and possible embodiments, the copolymerization method includes:

[0016] Under nitrogen protection and at a temperature of 8-10°C, an initiator is added to the mixture of acrylamide, heat-resistant monomer, and monomer that works synergistically with divalent metal ions, and the polymerization reaction is carried out for 5-8 hours.

[0017] In this disclosure and possible embodiments, the initiator is a redox initiator, and the amount of the initiator is 7 × 10⁻⁶. -6 g / mL -1.2×10 -5 g / mL.

[0018] In this disclosure and possible embodiments, the redox initiator includes an oxidant and a reducing agent, wherein the oxidant is any mixture of one or more of potassium persulfate, ammonium persulfate, sodium persulfate and hydrogen peroxide, and the reducing agent is any mixture of one or more of thiourea, sodium sulfite and sodium bisulfite.

[0019] The beneficial effects of this invention are as follows:

[0020] The environmentally responsive polymer disclosed herein for high-temperature, low-calcium reservoirs has the following characteristics compared to existing technologies:

[0021] (1) Improved stability: The polymer of the present invention has good thermal stability under high temperature conditions, and can maintain stable performance in high temperature environment. It is not easy to cause molecular structure damage or degradation, thereby ensuring long-term stable use in high temperature reservoirs.

[0022] (2) Improved viscosity enhancement: Compared with heat-resistant and salt-resistant polymers, the polymer of the present invention has a better viscosity enhancement effect and can form a more stable high-viscosity polymer solution in the reservoir environment, effectively improving the water-oil mobility ratio and increasing the oil displacement efficiency.

[0023] (3) Environmental responsive characteristics: This invention makes full use of the small amount of divalent metal ions in the reservoir environment. Through the synergistic effect of divalent metal ions and polymers, a thickening effect is achieved, turning unfavorable conditions into favorable conditions and improving the application performance of polymers in high-temperature and low-calcium reservoirs.

[0024] In summary, this invention has achieved significant improvements in the thermal stability, thickening effect, environmental responsiveness, and temperature resistance of polymers, providing a novel and efficient polymer for oil displacement in the development of high-temperature, low-calcium reservoirs. Detailed Implementation

[0025] 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.

[0026] 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."

[0027] To address the problems described in the background art, the technical concept of the environmentally responsive polymer for high-temperature, low-calcium reservoirs provided by this invention is that, for high-temperature, low-calcium reservoirs, the research and development focus of the polymer for oil displacement is on optimizing its own molecular structure, primarily responding to the reservoir environment, and fully utilizing the small amount of divalent metal ions (Ca) in the reservoir environment while ensuring good solubility. 2+ and Mg 2+ By leveraging the synergistic effect between divalent metal ions and polymers, a thickening effect is achieved, enabling the polymers to exhibit superior viscosity and temperature resistance under these reservoir conditions, thus transforming unfavorable conditions into favorable ones through environmental response.

[0028] Furthermore, the excellent thickening and temperature resistance of the environmentally responsive polymer used in high-temperature, low-calcium oil reservoirs in this invention stems from the polymer's molecular structure design. It is synthesized by copolymerizing a small amount of polymerizable monomers and temperature-resistant monomers that can form synergistic effects with divalent metal ions with acrylamide. Its molecular structure is shown in the following formula:

[0029]

[0030] The heat-resistant unit is a polymerizable monomer with heat-resistant properties, which can improve the stability and tolerance of the polymer in high-temperature environments. The unit that works synergistically with divalent metal ions can enhance the stability of the polymer in reservoir environments.

[0031] In one specific embodiment, the component composition ratio of the environmentally responsive polymer for high-temperature, low-calcium reservoirs, in molar percentages, is as follows: heat-resistant monomer: 1.5 mol%-3.5 mol%, acrylamide: 80 mol%-91 mol%, monomer synergistic with divalent metal ions: 7 mol%-18 mol%, and the balance being water.

[0032] The environmentally responsive polymer of this invention is suitable for high-temperature, low-calcium reservoirs with reservoir temperatures of 80℃-95℃, salinity not exceeding 6000mg / L, and calcium and magnesium ion concentrations not exceeding 100mg / L.

[0033] In one specific embodiment, the heat-resistant monomer may be selected from one or more of N-vinylpyrrolidone, N,N-dimethylacrylamide, sodium styrene sulfonate, sodium 2-acrylamido-2-methylpropanesulfonate, N-phenylethyl-N-dodecylmethylacrylamide, and N-dodecylacrylamide, or any mixture thereof.

[0034] In one specific embodiment, the monomer that synergizes with divalent metal ions can be selected from one or more of acrylic acid, sodium acrylate, methacrylic acid, sodium methacrylate, and maleic acid.

[0035] In this disclosure, the method for obtaining the polymer of the present invention by copolymerization using acrylamide, a heat-resistant monomer, and a monomer that synergizes with divalent metal ions is as follows:

[0036] Under nitrogen protection, at 8-10°C, an initiator is added to a mixture of the above three monomers, and a polymerization reaction is carried out for 5-8 hours to obtain the polymer of the present invention.

[0037] In one specific embodiment, the initiator is a redox initiator, and the amount of initiator used is 7 × 10⁻⁶. -6 g / mL -1.2×10 -5 g / mL; the redox initiator includes an oxidant and a reducing agent. The oxidant can be any mixture of one or more of potassium persulfate, ammonium persulfate, sodium persulfate and hydrogen peroxide, and the reducing agent can be any mixture of one or more of thiourea, sodium sulfite and sodium bisulfite.

[0038] All components used in the synthesis of environmentally responsive polymers for high-temperature, low-calcium oil reservoirs in the various embodiments of the present invention are commercially available products.

[0039] The following are the steps for evaluating the viscosity retention rate of the environmentally responsive polymers synthesized in various embodiments of the present invention for high-temperature, low-calcium reservoirs, and the comparative polymer solutions under certain high-temperature, low-calcium reservoir conditions:

[0040] (1) At room temperature, the polymer to be evaluated was added to simulated formation water in a high-temperature, low-calcium reservoir at a mass ratio of 0.06%-0.12% (see Table 1 for specific composition) and stirred for 2 hours. The solution was then measured using a Brookfield viscometer with rotor No. 0 (6 rpm, 7.3 s). -1 The apparent viscosity at 85℃ was 13 mPa·s-14 mPa·s.

[0041] (2) Put 50 mL of the solution from step (1) into a 50 mL ampoule, deoxygenate and fill with nitrogen at room temperature, and then sinter and seal the mouth of the ampoule.

[0042] (3) Place the ampoule from step (2) above into an 85°C oven and let it stand.

[0043] (4) After 30 days, take out the ampoule from step (3) and use a Brookfield viscometer with rotor No. 0 (6 rpm, 7.3 s⁻¹, 85 °C) to test the apparent viscosity of the solution and calculate the viscosity retention rate.

[0044] Table 1 Simulated water composition of high-temperature, low-calcium oil reservoirs

[0045]

[0046] The following are preferred embodiments and comparative examples of the present invention, wherein the polymer compositions and names of each comparative example and embodiment are as follows:

[0047] 1. Comparative Example 1:

[0048] HPAM, with a molecular weight of 16 million to 19 million, has 23.0 mol% sodium acrylate units and 77.0 mol% acrylamide units, and is referred to as HPAM1600 in this article.

[0049] 2. Comparative Example 2:

[0050] HPAM, with a molecular weight of 25 million, has 23.0 mol% sodium acrylate units and 77.0 mol% acrylamide units, and is referred to as HPAM2500 in this paper.

[0051] 3. Comparative Example 3:

[0052] Salt-resistant polymer 1, which has 11.7 mol% salt-resistant unit (sodium 2-acrylamido-2-methylpropanesulfonate, AMPSNa) and 88.3 mol% acrylamide unit, with a molecular weight of 13 million, is referred to as AP30 in this paper.

[0053] 4. Comparative Example 4:

[0054] Salt-resistant polymer 2 has 1.6 mol% of salt-resistant unit AMPSNa, 21.5 mol% of sodium acrylate unit, 76.9 mol% of acrylamide unit, and a molecular weight of 25 million, and is referred to as DS2500 in this article;

[0055] 5. Example 1:

[0056] The environmentally responsive polymer 1 used in high-temperature, low-calcium reservoirs has a heat-resistant unit (AMPSNa) of 1.6 mol%, a divalent metal ion synergistic unit (sodium acrylate unit) of 17.8 mol%, an acrylamide unit of 80.6 mol%, and a molecular weight of 25 million. It is referred to as DQ-1 in this paper.

[0057] 6. Example 2:

[0058] The environmentally responsive polymer 2 used in high-temperature, low-calcium reservoirs has a heat-resistant unit (AMPSNa) of 1.6 mol%, a divalent metal ion synergistic unit (sodium acrylate unit) of 13.4 mol%, an acrylamide unit of 85.0 mol%, and a molecular weight of 19 million. It is referred to as DQ-2 in this paper.

[0059] 7. Example 3:

[0060] The environmentally responsive polymer 3 used in high-temperature, low-calcium reservoirs has a heat-resistant unit (AMPSNa) of 1.6 mol%, a divalent metal ion synergistic unit (sodium acrylate unit) of 8.2 mol%, acrylamide unit of 90.2 mol%, and a molecular weight of 13 million. It is referred to as DQ-3 in this article.

[0061] 8. Example 4:

[0062] The environmentally responsive polymer 4 used in high-temperature, low-calcium reservoirs has a heat-resistant unit (AMPSNa) of 3.3 mol%, a divalent metal ion synergistic unit (sodium acrylate unit) of 7.3 mol%, an acrylamide unit of 89.4 mol%, and a molecular weight of 14 million. It is referred to as DQ-4 in this paper.

[0063] The preparation methods of the environmentally responsive polymers for high-temperature, low-calcium oil reservoirs described in Examples 1-4 above are as follows:

[0064] Under nitrogen protection and at 8°C, potassium persulfate and sodium bisulfite (mass ratio 7:3) were added as initiators to a mixture of the three monomers constituting the polymer. The amount of initiator used was 1.0 × 10⁻⁶. -5 g / mL; the polymerization reaction was carried out for 5 hours to obtain the environmentally responsive polymers of Examples 1 to 4 above.

[0065] The viscosity retention rates of the polymers in each embodiment and comparative example were evaluated and tested. The specific test methods are as follows, and the test results are shown in Table 2:

[0066] 1. Comparative Test Example 1:

[0067] A DQ-2 solution with a concentration of 800 mg / L was prepared using a NaCl solution with a mineralization of 3086 mg / L. The apparent viscosity of this solution at 85℃ was 13.5 mPa·s. The viscosity retention rate at 85℃ for 30 days was tested using the experimental procedures listed above. The apparent viscosity of the solution after 30 days was 7.2 mPa·s, and its viscosity retention rate after 30 days was 53.3%.

[0068] 2. Test Example 1:

[0069] A DQ-2 solution with a concentration of 800 mg / L was prepared using a solution with a mineralization of 3086 mg / L (containing 20 mg / L calcium ions, 5 mg / L magnesium ions, and the remainder being NaCl). The apparent viscosity of this solution at 85℃ was 13.2 mPa·s. The viscosity retention rate at 85℃ for 30 days was tested using the experimental procedures listed above. The apparent viscosity of the solution after 30 days was 18.0 mPa·s, and its 30-day viscosity retention rate was 136.4%.

[0070] 3. Comparative Test Example 2:

[0071] A 750 mg / L HPAM1600 solution was prepared using simulated water from a high-temperature, low-calcium reservoir with a salinity of 3086 mg / L, as shown in Table 1. The apparent viscosity of this solution at 85°C was 13.2 mPa·s. The viscosity retention rate at 85°C for 30 days was tested using the experimental procedures listed above. The apparent viscosity of the solution after 30 days was 8.6 mPa·s, and its viscosity retention rate after 30 days was 65.2%.

[0072] 4. Test Example 2:

[0073] A DQ-4 solution with a concentration of 1120 mg / L was prepared using simulated water from a high-temperature, low-calcium reservoir with a salinity of 3086 mg / L, as shown in Table 1. The apparent viscosity of this solution at 85℃ was 13.8 mPa·s. The viscosity retention rate at 85℃ for 30 days was tested using the experimental procedures listed above. The apparent viscosity of the solution after 30 days was 26.5 mPa·s, and its viscosity retention rate after 30 days was 192.0%.

[0074] 5. Comparative Test Example 3-1:

[0075] A 670 mg / L HPAM2500 solution was prepared using simulated water from a high-temperature, low-calcium oil reservoir with a salinity of 3086 mg / L, as shown in Table 1. The apparent viscosity of this solution at 85℃ was 13.8 mPa·s. The viscosity retention rate at 85℃ for 30 days was tested using the experimental procedures listed above. The apparent viscosity of the solution after 30 days was 8.7 mPa·s, and its viscosity retention rate after 30 days was 63.0%.

[0076] 6. Comparative test example 3-2:

[0077] A DS2500 solution with a concentration of 600 mg / L was prepared using simulated water from a high-temperature, low-calcium oil reservoir with a salinity of 3086 mg / L as shown in Table 1. The apparent viscosity of this solution at 85℃ was 13.6 mPa·s. The viscosity retention rate at 85℃ for 30 days was tested using the experimental procedures listed above. The apparent viscosity of the solution after 30 days was 10.1 mPa·s, and its viscosity retention rate after 30 days was 74.3%.

[0078] 7. Test Example 3:

[0079] A DQ-1 solution with a concentration of 660 mg / L was prepared using simulated water from a high-temperature, low-calcium oil reservoir with a salinity of 3086 mg / L as shown in Table 1. The apparent viscosity of this solution at 85℃ was 13.3 mPa·s. The viscosity retention rate at 85℃ for 30 days was tested using the experimental procedures listed above. The apparent viscosity of the solution after 30 days was 13.8 mPa·s, and its viscosity retention rate after 30 days was 103.8%.

[0080] 8. Comparative Test Example 4:

[0081] An AP30 solution with a concentration of 960 mg / L was prepared using simulated water from a high-temperature, low-calcium oil reservoir with a salinity of 3086 mg / L as shown in Table 1. The apparent viscosity of this solution at 85℃ was 13.3 mPa·s. The viscosity retention rate at 85℃ for 30 days was tested using the experimental procedures listed above. The apparent viscosity of the solution after 30 days was 1.0 mPa·s, and its viscosity retention rate after 30 days was 7.5%.

[0082] 9. Test Example 4:

[0083] A DQ-3 solution with a concentration of 980 mg / L was prepared using simulated water from a high-temperature, low-calcium oil reservoir with a salinity of 3086 mg / L as shown in Table 1. The apparent viscosity of this solution at 85℃ was 13.5 mPa·s. The viscosity retention rate at 85℃ for 30 days was tested using the experimental procedures listed above. The apparent viscosity of the solution after 30 days was 20.3 mPa·s, and its viscosity retention rate after 30 days was 150.4%.

[0084] Table 2 Viscosity retention rates of comparative and example samples at 85°C for 30 days

[0085]

[0086]

[0087] In Table 2, it is noted that Test Example 1 used a 3086 mg / L NaCl solution to prepare the DQ-2 solution, while Test Example 1 used a solution with a mineralization of 3086 mg / L (containing 20 mg / L calcium ions, 5 mg / L magnesium ions, and the remainder being NaCl) to prepare the DQ-2 solution. Clearly, the small amount of divalent metal ions (Ca) in the reservoir environment of Test Example 1 is significantly lower. 2+ and Mg 2+ The test results show that the viscosity retention rate of Test Example 1 is much higher than that of the control Test Example 1. This comparison demonstrates that fully utilizing the small amount of divalent metal ions (Ca) in the reservoir environment is beneficial. 2+ and Mg 2+ It can leverage the synergistic effect between divalent metal ions and polymers to achieve a thickening effect, enabling the polymer to exhibit superior viscosity and temperature resistance under these reservoir conditions.

[0088] Comparative Test Example 2 used a solution with a salinity of 3086 mg / L (containing 20 mg / L calcium ions, 5 mg / L magnesium ions, and the remainder NaCl) to prepare HPAM1600 solution. Test Example 2 used the same solution to prepare DQ-4 solution. Clearly, the molecular weight of HPAM1600 in Comparative Test Example 2 is 16-19 million, while the molecular weight of DQ-4 in Test Example 2 is 14 million. The comparison of the test results shows that the viscosity retention rate of Test Example 2 is much higher than that of Comparative Test Example 2. This comparison demonstrates that fully utilizing the small amount of divalent metal ions (Ca) in the reservoir environment is beneficial. 2+ and Mg 2+ This can overcome the disadvantage of low molecular weight and leverage the synergistic effect between divalent metal ions and polymers to achieve a thickening effect, enabling the polymer to exhibit superior viscosity and temperature resistance under these reservoir conditions.

[0089] Comparative Test Example 3-1 used a solution with a salinity of 3086 mg / L (containing 20 mg / L calcium ions, 5 mg / L magnesium ions, and the remainder NaCl) to prepare HPAM2500 solution. Comparative Test Example 3-2 used the same solution to prepare DS2500 solution, and Test Example 3 used the same solution to prepare DQ-1 solution. Clearly, the molecular weight of HPAM2500 in Comparative Test Example 3-1 is the same as that of DQ-1 in Test Example 3. Similarly, the molecular weight and AMPSNa content of DS2500 in Comparative Test Example 3-2 are the same as those of DQ-1 in Test Example 3. The test results show that the viscosity retention rate of Test Example 3 is significantly higher than that of Comparative Test Examples 3-1 and 3-2. This comparison demonstrates that fully utilizing the small amount of divalent metal ions (Ca) in the reservoir environment is beneficial. 2+ and Mg 2+ This allows the polymer to achieve a thickening effect by leveraging the synergistic effect between divalent metal ions and the polymer, resulting in superior viscosity and temperature resistance in this type of reservoir.

[0090] Comparative Test Example 4 used a solution with a salinity of 3086 mg / L (containing 20 mg / L calcium ions, 5 mg / L magnesium ions, and the remainder being NaCl) to prepare AP30 solution. Test Example 4 used the same solution to prepare DQ-3 solution. Clearly, the AMPSNa content of AP30 in Comparative Test Example 4 was much higher than that of DQ-3 in Test Example 4. The comparison of test results shows that the viscosity retention rate of Test Example 4 was much higher than that of Comparative Test Example 4. This comparison demonstrates that fully utilizing the small amount of divalent metal ions (CaCl₂, CaCl₃, and NaCl) in the reservoir environment is beneficial. 2+ and Mg 2+It can leverage the synergistic effect between divalent metal ions and polymers to achieve a thickening effect, enabling the polymer to exhibit superior viscosity and temperature resistance under these reservoir conditions.

[0091] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, and are not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical applications, or technical improvements to the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. An environmentally responsive polymer for high-temperature, low-calcium oil reservoirs, characterized in that, The components, measured by molar percentage, include: Temperature-resistant monomers: 1.5 mol%-3.5 mol%, acrylamide: 80 mol%-91 mol%, monomers that synergize with divalent metal ions: 7 mol%-18 mol%, balance is water.

2. The environmentally responsive polymer for high-temperature, low-calcium oil reservoirs according to claim 1, characterized in that: The high-temperature, low-calcium oil reservoir has a reservoir temperature of 80℃-95℃, a mineralization of no more than 6000 mg / L, and a calcium and magnesium ion concentration of no more than 100 mg / L.

3. The environmentally responsive polymer for high-temperature, low-calcium oil reservoirs according to claim 1 or 2, characterized in that: The heat-resistant monomer is selected from one or more of N-vinylpyrrolidone, N,N-dimethylacrylamide, sodium styrene sulfonate, sodium 2-acrylamido-2-methylpropanesulfonate, N-phenylethyl-N-dodecylmethylacrylamide, and N-dodecylacrylamide, or any mixture thereof.

4. The environmentally responsive polymer for high-temperature, low-calcium oil reservoirs according to claim 3, characterized in that: The monomer that synergizes with divalent metal ions is selected from one or more of acrylic acid, sodium acrylate, methacrylic acid, sodium methacrylate, and maleic acid.

5. A method for preparing the environmentally responsive polymer according to any one of claims 1-4, characterized in that, include: Acrylamide, a heat-resistant monomer, and a monomer that synergizes with divalent metal ions are copolymerized to obtain the environmentally responsive polymer.

6. The method for preparing the environmentally responsive polymer according to claim 5, characterized in that, The copolymerization method includes: Under nitrogen protection and at a temperature of 8-10°C, an initiator is added to the mixture of acrylamide, heat-resistant monomer, and monomer that works synergistically with divalent metal ions, and the polymerization reaction is carried out for 5-8 hours.

7. The method for preparing the environmentally responsive polymer according to claim 6, characterized in that: The initiator is a redox initiator, and the amount of initiator used is 7 × 10⁻⁶. -6 g / mL -1.2×10 -5 g / mL.

8. The method for preparing the environmentally responsive polymer according to claim 7, characterized in that: The redox initiator includes an oxidant and a reducing agent. The oxidant is one or a mixture of several of potassium persulfate, ammonium persulfate, sodium persulfate, and hydrogen peroxide. The reducing agent is one or a mixture of several of thiourea, sodium sulfite, and sodium bisulfite.

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