pH-responsive polymers, pH-responsive sols, pH-responsive gels, and methods of making and using

Abstract

The application discloses a pH-responsive polymer, a pH-responsive sol, a pH-responsive gel and a preparation method and application. After acrylamide, a response monomer and 3-[[2-(acryloyloxy)ethyl]dimethylammonio]undecanoate are dissolved in deionized water, the application is reacted with a thermal initiator in a CO2 environment, aqueous solution polymerization is carried out, and after drying and granulation, the pH-responsive polymer is obtained. The pH-responsive polymer is dissolved in deionized water with a small-molecule anionic crosslinking agent to obtain the pH-responsive sol. The application utilizes the electrostatic interaction between the tertiary amine group of the response monomer and the carboxylic acid group on the small-molecule anionic surfactant in a specific pH range to realize the self-assembly between molecules, is beneficial to the hydrophobic association of the hydrophobic tail chain of the small-molecule crosslinking agent to realize gelation, and realizes deep profile control on an oil reservoir.

Description

Technical Field

[0001] The present invention relates to the field of petroleum extraction, and in particular to a pH-responsive polymer, a pH-responsive sol, a pH-responsive gel, and a preparation method and application thereof. Background Art

[0002] Profile control is an important method for enhancing oil recovery. By plugging existing advantageous channels in the reservoir, subsequent displacement fluids are facilitated to enter low-porosity, low-permeability areas, enabling crude oil extraction in these areas. Currently, deep profile control is a major challenge in this process, particularly how to seal the plugging agent deep within the reservoir. Existing solutions for deep profile control include delayed gelation and smart gelation. Delayed gelation involves dissolving a polymer and a retarding crosslinking agent in an aqueous solution and co-injecting them into the reservoir. This slowly gels at reservoir temperatures, achieving delayed crosslinking. However, due to the high viscosity of the polymer solution, injection is generally difficult, resulting in additional equipment requirements and economic costs. Smart gels are gel materials with specialized properties, typically created by adding or embedding smart materials or functional units into a base gel. Smart gels adjust the gel's morphology, structure, or performance through environmental changes such as pH, light, electricity, magnetism, and CO2. Conventional photo-, electrical-, and magnetic-responsive materials are not feasible for the application of smart gels in reservoirs. Therefore, it is of great significance to provide an intelligent plugging solution based on pH adjustment to achieve sol-to-gel transition for deep reservoir profile control. Summary of the Invention

[0003] To address the above-mentioned technical problems, the present invention provides a pH-responsive polymer, a pH-responsive sol, a pH-responsive gel, and preparation methods and applications. The present invention is suitable for deep oilfield profile control. By adjusting the pH of the injected solution, the sol system forms a gel deep within the reservoir, promoting the bypass of subsequent displacement fluids into unaffected areas, thereby achieving profile control and improving oil recovery.

[0004] In a first aspect, the present invention provides a pH-responsive polymer, which is achieved by adopting the following technical solution.

[0005] A pH responsive polymer is copolymerized by the following monomers in molar percentages: 19.5-4.5% of a responsive monomer, 80-95% of acrylamide, and 0.5% of 3-[[2-(acryloyloxy)ethyl]dimethylammonium]undecane-1-carboxylate (DMAC11).

[0006] Furthermore, the response monomer is selected from any one of dimethylaminoethyl methacrylate, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide, N-methoxy-2,N-dimethylacrylamide and dimethylaminopropylacrylamide.

[0007] In a second aspect, the present invention provides a method for preparing a pH-responsive polymer, which is achieved by adopting the following technical solution.

[0008] A method for preparing the above-mentioned pH-responsive polymer comprises the following steps: dissolving a responsive monomer, acrylamide and 3-[[2-(acryloyloxy)ethyl]dimethylammonium]undecane-1-carboxylate in deionized water, introducing CO2 to remove O2, adjusting the pH to 4-5, adding an initiator azobisisobutylamidine hydrochloride, polymerizing at 50°C for 4-5h, and obtaining a pH-responsive polymer after granulation and drying.

[0009] By adopting the above technical solution, the initiator azobisisobutylamidine hydrochloride decomposes at the reaction temperature to form free radicals as active intermediates, and the free radicals attack double bonds to form new free radicals to form a chain reaction to form a long-chain polymer.

[0010] Furthermore, the monomer accounts for 20-30% of the aqueous solution by mass.

[0011] Furthermore, in terms of mass percentage, the initiator azobisisobutylamidine hydrochloride accounts for 0.3 to 0.8% of the mass of the monomer.

[0012] In a third aspect, the present invention provides a pH-responsive sol, which is achieved by adopting the following technical solution.

[0013] A pH responsive sol comprises the following raw materials in weight percentage: 0.4-1 wt% of the pH responsive polymer, 0.05-0.2 wt% of a small molecule anionic cross-linking agent, and the balance being water.

[0014] By adopting the above technical solution, a pH-responsive polymer and a small molecule anionic crosslinker are blended to form a sol. The liquid form and low viscosity of the sol facilitate the reservoir injectability of the pH-responsive sol. The pH-responsive sol has a low initial viscosity of 15 to 53 mPa.s at 25°C.

[0015] Furthermore, the small molecule anionic crosslinking agent includes sodium dodecylbenzenesulfonate, sodium sulfonate with a carbon chain length of 10 to 14, and sodium carboxylate with a carbon chain length of 12 to 14.

[0016] Preferably, the sodium sulfonate with a carbon chain length of 10 to 14 is selected from sodium dodecylsulfonate and sodium tetradecylsulfonate.

[0017] Preferably, the sodium salt of carboxylate with a carbon chain length of 12 to 14 is selected from sodium lauryl carboxylate and sodium tetradecyl carboxylate.

[0018] In a fourth aspect, the present invention provides a use of a pH-responsive sol, which is achieved by adopting the following technical solution.

[0019] An application of the pH-responsive sol in deep reservoir profile control.

[0020] Furthermore, the pH value of the pH-responsive sol is adjusted to a pH value range for sol-to-gel transition by a pH regulator to form a pH-responsive gel; the pH value range for sol-to-gel transition is 5-7.

[0021] By adopting this technical solution, the tertiary amine groups in the pH-responsive polymer in the solution are protonated within the pH range of the sol-to-gel transition. They then connect to the anionic groups on the small molecule anionic crosslinker through electrostatic attraction. Simultaneously, the hydrophobic tails of the small molecule anionic crosslinker crosslink through hydrophobic association to form a three-dimensional network structure, achieving the sol-to-gel transition. The pH-responsive gel formed from the pH-responsive sol has a viscosity of 5,000 to 120,000 mPa.s at 25 to 70°C.

[0022] Specifically, the pH adjuster is a 0.1 mol / L hydrochloric acid solution.

[0023] Furthermore, under the action of an alkaline regulator, the pH value of the pH-responsive gel is adjusted to a pH range where the gel transforms into a sol, thereby achieving a reversible transformation of the pH-responsive gel; the pH value where the gel transforms into a sol is 8 to 14.

[0024] By adopting this technical solution, the alkaline regulator interacts with the tertiary amine groups of the pH-responsive polymer in the pH-responsive gel, reducing the protonated tertiary amine groups to deprotonated tertiary amine groups. This eliminates the electrostatic interaction between the small molecule anionic crosslinker and the pH-responsive polymer, achieving a reversible transformation from the pH-responsive gel to a pH-responsive sol. The pH-responsive sol, transformed from the pH-responsive gel, has a viscosity of 5 to 35 mPa·s at 25 to 70°C.

[0025] Specifically, the alkaline regulator is a 0.1 mol / L sodium hydroxide solution.

[0026] In a fourth aspect, the present invention provides a pH-responsive gel, which is achieved by adopting the following technical solutions.

[0027] A pH-responsive gel is prepared by adjusting the pH value of the pH-responsive sol to 5 to 7. The pH-responsive gel has a viscosity of 5,000 to 120,000 mPa.s at 25 to 70°C.

[0028] This application has the following beneficial effects.

[0029] The present invention copolymerizes pH-responsive monomers, acrylamide, and 3-[[2-(acryloyloxy)ethyl]dimethylammonium]undecane-1-carboxylate to prepare a pH-responsive polymer. The pH-responsive polymer and a small molecule anion crosslinker are prepared into an aqueous solution in a certain proportion to obtain a low-viscosity pH-responsive sol system. By adjusting the pH value of the sol system, the sol is transformed into a sol. The low-viscosity sol system ensures its injection performance and deep migration ability as an injection fluid, and the sol-to-gel transformation under pH adjustment realizes the blocking of deep hypertonic areas. The present invention provides an intelligent blocking solution for deep reservoir profile adjustment based on pH adjustment to achieve sol-to-gel transformation. Through the action of pH-responsive polymer and small molecule anion crosslinker, the injectability problem faced in deep profile adjustment is solved; through the stimulation of acid solution to achieve gelation, the deep gelation problem faced in deep profile adjustment is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 3D network structure diagram of the pH-responsive gel after the pH-responsive sol in Example 1 of the present invention is transformed into the pH-responsive gel at a pH of 5.5;

[0031] Figure 2 This is a graph showing the viscosity of the pH-responsive gel at 25° C. to 70° C. after the pH-responsive sol in Example 1 of the present invention is converted into a pH-responsive gel at a pH of 5.5;

[0032] Figure 3 This is a microscopic morphology of the sol after the pH-responsive gel in Example 1 of the present invention is transformed into a pH-responsive sol at a pH of 9;

[0033] Figure 4 This is a graph showing the viscosity of the pH-responsive gel at 25° C. to 70° C. after the pH-responsive sol in Example 2 of the present invention is converted into a pH-responsive gel at a pH of 6;

[0034] Figure 5 This is a graph showing changes in injection pressure during a core flooding experiment in the performance test of the present invention;

[0035] Figure 6 It is a schematic diagram of the preparation process of the pH responsive gel of the present invention. DETAILED DESCRIPTION

[0036] The present patent application is further described below with reference to the embodiments.

[0037] DMAC11, used in the following examples of the present invention, is prepared from DMAEMA (dimethylaminoethyl methacrylate) and 11-bromodecaneonic acid, both purchased from Shanghai Aladdin Biotechnology Co., Ltd. (98%). The preparation method is as follows: 2.50 g of dimethylaminoethyl methacrylate (DMAEMA) and 5.05 g of 11-bromodecaneonic acid are added to a three-necked flask at a molar ratio of 1:1.2, using 100 mL of anhydrous ethanol as the solvent and 0.2 g of potassium iodide as the catalyst. Nitrogen is passed through the flask for 30 minutes to remove oxygen. The reaction is carried out under nitrogen protection in a constant temperature water bath at 35°C with magnetic stirring for 72 hours. The product solution is filtered, the ethanol is removed under reduced pressure, and the crude product is dried at 35°C for 24 hours. The dried crude product is dissolved in water and extracted three times with diethyl ether. The resulting aqueous phase is freeze-dried to yield a white powder, namely 2-methacryloyloxyethyldimethyl-11-undecanoic acid ammonium bromide (DMAC11).

[0038] Example 1

[0039] A method for preparing a pH-responsive gel comprises the following steps:

[0040] A monomer containing 20 g of dimethylaminoethyl methacrylate, acrylamide (AM) and DMAC11 in a molar ratio of 9.5:90:0.5 was dissolved in 80 g of deionized water, CO2 was introduced to remove O2 and the pH was adjusted to 4.5. 0.1 g of azobisisobutylamidine hydrochloride was added and polymerized at 50 °C for 4 h. After granulation and drying, a pH-responsive polymer was obtained.

[0041] A pH-responsive sol was prepared containing 0.6 wt % of a pH-responsive polymer and 0.11 wt % of sodium dodecylbenzenesulfonate. The viscosity of the sol was 24 mPa.s at 25° C., which was suitable as a low-viscosity injection fluid.

[0042] The pH of the pH-responsive sol was adjusted to 5.5 using a pH regulator to obtain a pH-responsive gel. The viscosity of the gel at 25°C was 113,000 mPa.s. Figure 1 As shown in Figure 3, the pH-responsive gel has a dense three-dimensional network structure. Figure 2 As shown in the figure, with the increase of temperature, the viscosity of the gel gradually decreases. At 70°C, the viscosity decreases to 36400 mPa.s.

[0043] The pH value of the pH-responsive gel was adjusted to 9 using an alkaline regulator. Figure 3 As shown in the figure, the dense three-dimensional network structure of the pH-responsive gel gradually transforms into a sparse network structure. The viscosity of the sol at 25°C is 25 mPa.s. As the temperature increases, the viscosity of the sol gradually decreases, and at 70°C, the viscosity decreases to 23 mPa.s.

[0044] Example 2

[0045] A method for preparing a pH-responsive gel comprises the following steps:

[0046] A monomer containing 20 g of dimethylaminoethyl methacrylate, acrylamide (AM) and DMAC11 in a molar ratio of 19.5:80:0.5 was dissolved in 80 g of deionized water, CO2 was introduced to remove O2 and the pH was adjusted to 4.5. 0.12 g of azobisisobutylamidine hydrochloride was added and polymerized at 50 °C for 4 h. After granulation and drying, a pH-responsive polymer was obtained.

[0047] A pH-responsive sol was prepared containing 0.4 wt % of a pH-responsive polymer and 0.06 wt % of sodium dodecyl sulfate. The viscosity of the sol was 32 mPa.s at 25° C., which was suitable as a low-viscosity injection fluid.

[0048] The pH value of the pH-responsive sol was adjusted to 6 using a pH regulator to obtain a pH-responsive gel. The viscosity of the gel at 25°C was 31300 mPa.s. Figure 4 As shown in the figure, with the increase of temperature, the viscosity of the gel gradually decreases. At 70°C, the viscosity decreases to 7300 mPa.s.

[0049] The pH value of the pH-responsive gel was adjusted to 9 using an alkaline regulator. The viscosity of the sol was 29 mPa.s at 25°C. The viscosity of the sol gradually decreased with increasing temperature, and at 70°C, the viscosity dropped to 27 mPa.s.

[0050] Example 3

[0051] A method for preparing a pH-responsive gel comprises the following steps:

[0052] A monomer containing 20 g of N,N-dimethylmethacrylamide, acrylamide (AM) and DMAC11 in a molar ratio of 14.5:85:0.5 was prepared and dissolved in 80 g of deionized water. CO2 was introduced to remove O2 and the pH was adjusted to 4.5. 0.14 g of azobisisobutylamidine hydrochloride was added and polymerized at 50°C for 4 h. After granulation and drying, a pH-responsive polymer was obtained.

[0053] A pH-responsive sol was prepared containing 0.4 wt % of a pH-responsive polymer and 0.07 wt % of sodium tetradecylcarboxylate. The viscosity of the sol was 26 mPa.s at 25° C., which was suitable as a low-viscosity injection fluid.

[0054] The pH of the pH-responsive sol was adjusted to 6.5 using a pH regulator, yielding a pH-responsive gel. The gel exhibited a viscosity of 28,300 mPa.s at 25°C. The viscosity gradually decreased with increasing temperature, reaching 5,200 mPa.s at 70°C.

[0055] The pH value of the pH-responsive gel was adjusted to 11 using an alkaline regulator. The viscosity of the sol was 18 mPa.s at 25°C. As the temperature increased, the viscosity of the sol gradually decreased, reaching 17 mPa.s at 70°C.

[0056] Performance testing

[0057] The profile control performance of the pH-responsive gel in Example 1 was determined by core flooding experiments. Core size: 30*4.5*4.5 homogeneous, permeability: 2000 md.

[0058] like Figure 5 As shown, the first water flooding was started with a water flooding volume of 2 PV. After the water flooding pressure stabilized, it was 1.82 MPa. Then, 1 PV of pH-responsive sol was injected, and the injection pressure was increased to 2.90 MPa.

[0059] A secondary water flooding was carried out using an acid solution with a pH of 5 as the injection fluid. During the secondary water flooding process, the pressure value increased rapidly, with the maximum pressure value being 3.63 MPa. The above results show that the pH-responsive gel of the present invention can achieve deep profile control under acidic conditions.

[0060] The embodiments of this specific implementation method are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A pH-responsive sol, characterized in that: The method comprises the following raw materials in the following weight percentages: 0.4-1 wt% of a pH-responsive polymer, 0.05-0.2 wt% of a small molecule anionic crosslinker, and the balance being water; The pH-responsive polymer is copolymerized by the following monomers in molar percentages: 19.5-4.5% of a responsive monomer, 80-95% of acrylamide, and 0.5% of 3-[[2-(acryloyloxy)ethyl]dimethylammonio]undecane-1-carboxylate; the responsive monomer is selected from any one of dimethylaminoethyl methacrylate, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide, N-methoxy-2,N-dimethylacrylamide, and dimethylaminopropylacrylamide; Small molecule anionic crosslinking agents include sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, sodium tetradecylsulfonate, and sodium salts of carboxylates with a carbon chain length of 12 to 14.

2. A pH-responsive sol according to claim 1, characterized in that: The preparation method of the pH-responsive polymer includes the following steps: dissolving a responsive monomer, acrylamide and 3-[[2-(acryloyloxy)ethyl]dimethylammonium]undecane-1-carboxylate in deionized water, introducing CO2 to remove O2, adjusting the pH to 4-5, adding an initiator azobisisobutylamidine hydrochloride, polymerizing at 50°C for 4-5h, and obtaining a pH-responsive polymer after granulation and drying.

3. A pH-responsive sol according to claim 2, characterized in that: In terms of mass percentage, the monomer accounts for 20-30% of the aqueous solution.

4. Use of the pH-responsive sol according to any one of claims 1 to 3 in deep reservoir profile control.

5. The use according to claim 4, characterized in that: The pH value of the pH-responsive sol is adjusted to a pH value range where the sol transitions to a gel by a pH regulator, thereby forming a pH-responsive gel; the pH value range where the sol transitions to a gel is 5-7.

6. The use according to claim 5, characterized in that: Under the action of an alkaline regulator, the pH value of the pH-responsive gel is adjusted to a pH range where the gel transitions to a sol, thereby achieving a reversible transformation of the pH-responsive gel; the pH value where the gel transitions to a sol is 8-14.

7. A pH-responsive gel, characterized in that: The pH-responsive gel is prepared by adjusting the pH value of the pH-responsive sol according to any one of claims 1 to 3 to 5 to 7.

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